Classic & Vintage - wheel build advice

its been over a year since i bought the parts but i am finally ready to build my NOS wheelset. i intended to do it last year but other things occupied my time any finances (wedding, auto purchase, auto repairs)

i ended up selling the "old" wheels so now i am committed.

rider specs:
6'1"
175lbs

bike specs:
1996 tommasini tecno
campagnolo alloy mix
nice weather casual rides, centuries, charity rides

purchased parts:
NOS 28h chorus/athena front hub
http://i280.photobucket.com/albums/kk177/thirdgenbird/wheel%20build/Picture1.png
NOS 28h record 10 rear hub
http://i280.photobucket.com/albums/kk177/thirdgenbird/wheel%20build/hub.jpg
NOS 28h seoul 88 rims (602 ERD)
http://i280.photobucket.com/albums/kk177/thirdgenbird/wheel%20build/2010-09-08175355.jpg

spoke plans:
font
2x
dt revolution 1.8/1.5 (or sapim cxray)

rear
2x
dt competition 1.8/1.6 (or cxray) drive side
dt revolution 1.8/1.5 (or cxray) NDS


which of these if any do you recommend? will these be sufficiently stiff or should i go with heavier spokes?

i used two spoke calculators and got the same results but i still wouldnt mind someone checking my work:
http://i280.photobucket.com/albums/kk177/thirdgenbird/wheel%20build/Picture5.png

if anyone has any overall advice for wheel builds i am all ears. am i silly for tackling this without a tension gauge?

Based on my research, sapim spokes come highly recommended and that's what I'm going to use when I build a set of wheels. I doubt you need heavier spokes, if the rim is strong and they're laced correctly I doubt it's a problem. The sapims are supposedly pretty strong anyway.

This is also highly recommended: (look up reviews they're all extremely positive)

http://www.wheelpro.co.uk/wheelbuilding/book.php

Lastly if you feel like you need a tension gauge you can borrow mine if you want to pay for shipping there and back, I won't need it for a few weeks at least. I won a wheelsmith gauge on ebay for $20 a few months ago lol...

thanks!

the rims are very stout. they are the same as the old omega V. here is a quote from velobase:

Years ago Jobst Brandt did some rim stiffness tests and this rim was amongst the very best tested, exceeding that of the Zipp 808, which had just come out when Jobst was testing

ive read good things about the cxray spokes as well but cant decide if it is worth the extra cost


i may take you up on the tension gauge. im not sure when i will get the spoke order in but if i need it i will be in contact.

Casey,

First things first - screw you for owning that Record 28h hub. :drool:

Second - your build looks great for your weight. DT Rev spokes are fantastic, and I used them around my entire rear wheel as well as alloy nipples to go for a truly light set up. However, based on the fact that you power around on 180mm cranks, I'd say keep the Competitions on the drive side.

From my experience, DT outdoes Sapim by a tenfold margin in terms of quality and longevity - plus they're US-based. The only reason to go for Sapim is if you're building an aero wheel, and with 28spokes on front and rear, you're going to hit an aero block far before those spokes will have a chance to do you any good.

Third - unsure if you've built wheels before, but you DON'T need a spoke gauge. My experience with spoke gauges is that they can cause some pretty serious headaches that aren't really warranted when building a bicycle wheel.

Fourth - if you were closer to me, I'd volunteer to come help you out, but I have faith that you can do this. Wheel building is fun as hell and very meditative.

Fifth - as a side note, since those wheels don't have eyelets, I think you may need some nipple washers dependent on whatever spoke you choose.

if anyone has any overall advice for wheel builds i am all ears. am i silly for tackling this without a tension gauge?

This might be self evident to most, but having a real wheel truing stand makes this job immeasurably easier.
The second bit of advice is to focus on getting the wheel ROUND first - tensioning it gradually, and then deal with the lateral truing.

I don't think a tension gage is critical if you work slowly and evenly.

I've used Edd Spoke (http://lenni.info/edd/), Sapim Race spokes and chromed, brass nipples on several wheel builds lately and I'll use both for my next wheel build. I buy my spokes from this seller (http://www.ebay.com/sch/childhood_dreams/m.html?_dmd=1&_ipg=50&_sop=15&_rdc=1) (email (lkspoke@yahoo.com)). I would build them with cross 3 lacing. I've read and found The Bicycle Wheel (http://www.icelord.net/bike/thebicyclewheel.htm) and recommend it.

If they're anything like campy omega v rims they're gonna be strong. I have a set of those laced to mavic 501 hubs on my bianchi, I've taken some direct hits, crashed them, and they're still perfectly true. Anyhow it's up to you on the spokes, I dunno where you were planning on buying them from but this place probably has the best prices on sapim:

http://www.bikehubstore.com/Default.asp

Casey,

First things first - screw you for owning that Record 28h hub. :drool:

i payed a lot but it looks like they go for quite a bit more now. i gave up finding the matching front. the slimmer standard axle hub will look better at the end of a thin steel fork anyway...

Second - your build looks great for your weight. DT Rev spokes are fantastic, and I used them around my entire rear wheel as well as alloy nipples to go for a truly light set up. However, based on the fact that you power around on 180mm cranks, I'd say keep the Competitions on the drive side.

that is where i am leaning alloy nipples but brass on the drive side with comp spokes

From my experience, DT outdoes Sapim by a tenfold margin in terms of quality and longevity - plus they're US-based. The only reason to go for Sapim is if you're building an aero wheel, and with 28spokes on front and rear, you're going to hit an aero block far before those spokes will have a chance to do you any good.

Third - unsure if you've built wheels before, but you DON'T need a spoke gauge. My experience with spoke gauges is that they can cause some pretty serious headaches that aren't really warranted when building a bicycle wheel.

it will be my first build from scratch

Fourth - if you were closer to me, I'd volunteer to come help you out, but I have faith that you can do this. Wheel building is fun as hell and very meditative.

Fifth - as a side note, since those wheels don't have eyelets, I think you may need some nipple washers dependent on whatever spoke you choose.

this would change my spoke length correct?




This might be self evident to most, but having a real wheel truing stand makes this job immeasurably easier.
The second bit of advice is to focus on getting the wheel ROUND first - tensioning it gradually, and then deal with the lateral truing.

I don't think a tension gage is critical if you work slowly and evenly.

my dad as a decent truing stand that i have access to.

I've been using Edd Spoke (http://lenni.info/edd/), Sapim Race spokes and chromed, brass nipples on several wheel builds lately and I'll use both for my next wheel build. I buy my spokes from this seller (http://www.ebay.com/sch/childhood_dreams/m.html?_dmd=1&_ipg=50&_sop=15&_rdc=1) (email (lkspoke@yahoo.com)).

Edd Spoke was the other calculator i used. with the inputs above i got the same results as the DT swiss site. ive got screen ****s from there too.


If they're anything like campy omega v rims they're gonna be strong. I have a set of those laced to mavic 501 hubs on my bianchi, I've taken some direct hits, crashed them, and they're still perfectly true. Anyhow it's up to you on the spokes, I dunno where you were planning on buying them from but this place probably has the best prices on sapim:

http://www.bikehubstore.com/Default.asp

i will look into both retailers, thanks

when doing a build like this do you guys often buy spare spokes? would two of each length be sufficient?

I bought one spoke extra per side of each wheel for my first couple of builds. I've never needed one during building and the last few builds I haven't ordered extra. My LBS has spokes and a threader that can get the job done in a pinch if I need one.

My LBS has spokes and a threader that can get the job done in a pinch if I need one.

my LBS does have a threader but i was weary of cut vs rolled threads

Then order a few extra. We're not talking about a lot of money here.

more questions...

trailing spokes, where should they be? my bikes are all different.

should they be in or out on the drive side?

should the NDS be a mirror image (trailing spokes out on both non drive and drive) or should it be "copied" on the no drive side (out on the DS and in on the NDS)

i may have answered my own question as it looks like the pros choose to put the trailing spokes on the outside of both flanges for the paris roubaix


http://cdn0.media.cyclingnews.futurecdn.net/2011/04/13/2/parisroubaix_wheelsandtires_30_600.jpg
http://cdn.mos.bikeradar.com/images/news/2010/04/14/1271086249783-14gcjo7n0cn0u-670-75.jpg

Did you measure the ERD yourself? It makes a big difference. I recently built similar wheels 32F,36R Campy 10speed record Hubs, DT Swiss Competition Spokes, Mavic open pros.

http://i1128.photobucket.com/albums/m483/MichaelAngelo54/Gazelle/Athena3.jpg

http://i1128.photobucket.com/albums/m483/MichaelAngelo54/Gazelle/Athena4.jpg

http://i1128.photobucket.com/albums/m483/MichaelAngelo54/Gazelle/Athena5.jpg

Did you measure the ERD yourself? It makes a big difference.

no, two online sources list the ERD at 602mm. is there any way to verify this?

no, two online sources list the ERD at 602mm. is there any way to verify this?

I would trust that. But, yeah, you could measure the ERD. Remember to round down the spoke measurement to the nearest whole millimeter. Again, I really recommend reading The Bicycle Wheel before your first build. All of your questions can be answered there.

I try to measure out the ERD. With Open Pros, I think I measured out an additional 2 - 3mm to whats listed on the mavic site. Something about them measuring the spoke nipple bead differently?

I did measure the Open Pros I used they were ERD 603. The tool I made is very accurate. This is the spoke calculator I used http://www.wheelpro.co.uk/spokecalc/. The spoke lengths were perfect.

I did measure the Open Pros I used they were ERD 603. The tool I made is very accurate.

what are the chances you have access to a seoul 88/omega v rim :)

not that it manners for the build but i should also not that despite the fact i am using a non matched older front hub i did locate a matching front skewer. (as shown in your pictures) they are my favorite made.

my LBS does have a threader but i was weary of cut vs rolled threads

If its a Phil Wood machine the spoke is cut and then threads are rolled.....I've probably cut 30-40,000 spokes on a Phil machine


i may have answered my own question as it looks like the pros choose to put the trailing spokes on the outside of both flanges for the paris roubaix


http://cdn0.media.cyclingnews.futurecdn.net/2011/04/13/2/parisroubaix_wheelsandtires_30_600.jpg
http://cdn.mos.bikeradar.com/images/news/2010/04/14/1271086249783-14gcjo7n0cn0u-670-75.jpg

I remember reading a DT or Mavic tech article way back in the day that recommended the spoke heads for the drive spokes to be on the inside of the flange.

And...an ERD difference of +/- 2 isnt going to make and difference on a laced wheel. And a overall spoke length difference +/- 2 isnt going to make a difference either.

If its a Phil Wood machine the spoke is cut and then threads are rolled.....I've probably cut 30-40,000 spokes on a Phil machine



I remember reading a DT or Mavic tech article way back in the day that recommended the spoke heads for the drive spokes to be on the inside of the flange.

i havent seen it but i doubt it is a phil woods machine. it is a very tiny shop that doesnt do much for wheel building. i was shocked he had one as he doesnt have any frame prep tools. i also dont believe he has campagnolo cassette or chain tool

further research seems to show that european builders favor outboard trailing spokes while Americans prefer internal. prebuilt campy wheels all have outboard trailing spokes so i will stick with this model.

I know there are people that have reasons to put the trailing spoke heads on the outside, but I have had bad luck doing this. An informal survey shows that the vast majority of wheelbuilders put the the trailing spoke heads on the inside. I hope handspun does this because I just reused a hub out of one of their wheels and just followed the wear marks without checking. Gonna be mad if they did it wrong.

It's better to have a spoke thats a bit longer than to come up short.

http://i1128.photobucket.com/albums/m483/MichaelAngelo54/Gazelle/Athena4.jpg


When I count those cogs, I always think of Spinal Tap.

On the wheels, on vintage stuff, I place the "torque" spoke head out, on both sides. On a hub such as you have I would probably go the other way.

Lace and build the front wheel first. Do note that you do not want spokes "crossing the valve hole". I also agree that you work the roundness mostly at the beginning. I actually use a speed screwdriver, sometimes called a "yankee" driver to get the spokes to the same point fast. Without one, you might thread all the spokes to the same point to begin, if I am building a "new" to me wheel, and do not have spoke length notes, I start with 3 threads showing.

And for the nitpicky, keep the rim labels reading from the same side when mounted on the bike... I don't remember if these hubs have a "spin" direction with regard to the text on the hub body and or oil clips. Back in the old Record hub days that was part of a "pro" wheel. Much of the above will not effect engineering performance.

A truing stand does make the job go faster. A dishing tool also helps. Even those stands where the guides show zero dish.... I am just a test, don't guess kind of guy.
I have used the bike upside down with tape used to create a roundness gauge. What a cash strapped college student did to earn money building wheels long ago.

There are books that can be of assistance, but experience is just that, probably reading one of the wheelbuilding books after a wheel or two will be of more use.

Before you start calculating, you first need to decide:

1. What nipples you will use, 10mm standard profile, 12mm standard profile, or 14mm standard profile or 16mm standard profile.

2. What threads you will use (boxed at 9.0-9.5mm) or (Phil / Morizumi / Kowa Cutter 9.5mm-10.5mm).

3. Then you need to test the nipple and thread of your choice to determine how far the spoke can thread - and then what your aiming point for overhead will be.

http://www.youtube.com/watch?v=gCXFKN9JvCQ&context=C31932c8ADOEgsToPDskLaenuUwwH7Boe2oBRcEd-L

The video linked above explains why...there's a nifty chart at the end that summarizes how nipple and thread behavior affect the ERD you use for a given rim.

The overhead - usually 1.0m to 1.5mm is to ensure that you DO NOT run out of thread before achieving the desired tension.


Going on...

Campagnolo like Shimano does not measure their hubs the way spoke calculators expect...


Adjusted specs:

Athena / Chorus Front

Adding 1.6mm to flange each side to correct offset results in:

d = 38.5
c-offset = 34.10


Adding 1.6mm to each flange to correct offset results in:

Record Rear

d-left = 44.00
c-left-offset = 36.76

d-right = 46.00
d-right-offset = 16.80


Assuming the ERD of 602 does assume a standard profile 12mm nipple with an aim for the screwdriver flat:

Front = 290.39 - .30 = 290.00mm

Rear Left = 289.13 - .20 = 288.93mm (You could get away easily with 289.00mm )

Rear Right = 286.71 - .20 - 286.51mm (Round down drive side brings you to 286.00mm )


290.00, 289.00 and 286.00


Once again that assumes that the ERD already noted aims for the screwdriver flat of a standard profile 12mm nipple. Whoever gave you the number - go find out what their reference was. Damon Rinard and I publish our reference for our ERDs, many people don't.

=8-)

Someday I'll have to post pics of how I build wheels as I install all of the spokes first and then lace up the rim.

This is fun. Thanks for the link OP. You guys are WAY overthinking it. Get within 2mm and you're fine. After thousands of wheels - posted ERDs are just fine.

Lacing head out or head in for the trailing spoke on the DS is a personal choice and nothing more. Literally. Schraner does head in. Jobst does head out. I dare any of you to point at either one of those guys and tell them they're wrong.....because it doesn't matter which one you pick....you'll look like a fool. I have done both. It results in absolutely no difference in the end build. Pick a religion and then just stick with it.

OP - first build - no tensiometer - at 170+ in a 24/28 setup: use dt comps all around and be done with it. the revs are OK, but they are spongy and a bit more expensive - not to mention much harder for you as a consumer to find in the lenght you want for the qty you want. Most Distributors have stopped carrying Revs in their catalogs because of the small demand. Building with a rev as a first build you are going to have issues with spoke stretch and twist as it comes up to tension. Just go comps. Much better spoke, easy to build with and available in a myriad of lengths at any shop in near the whole world. Besides....if you get bored later you can just go re-lace them.

You guys are WAY overthinking it. Get within 2mm and you're fine. posted ERDs are just fine.

Lacing head out or head in for the trailing spoke on the DS is a personal choice and nothing more. Literally.

OP - first build - no tensiometer - .

That about sums it up.

This is fun. Thanks for the link OP. You guys are WAY overthinking it. Get within 2mm and you're fine. After thousands of wheels - posted ERDs are just fine.

Lacing head out or head in for the trailing spoke on the DS is a personal choice and nothing more. Literally. Schraner does head in. Jobst does head out. I dare any of you to point at either one of those guys and tell them they're wrong.....because it doesn't matter which one you pick....you'll look like a fool. I have done both. It results in absolutely no difference in the end build. Pick a religion and then just stick with it.

OP - first build - no tensiometer - at 170+ in a 24/28 setup: use dt comps all around and be done with it. the revs are OK, but they are spongy and a bit more expensive - not to mention much harder for you as a consumer to find in the lenght you want for the qty you want. Most Distributors have stopped carrying Revs in their catalogs because of the small demand. Building with a rev as a first build you are going to have issues with spoke stretch and twist as it comes up to tension. Just go comps. Much better spoke, easy to build with and available in a myriad of lengths at any shop in near the whole world. Besides....if you get bored later you can just go re-lace them.

Ummm...Psimet2001...

Overall we are not WAY overthinking it. ERD is very important. That number can be the deal killer where threads are concerned versus tension. I.e., if someone when calculating uses an ERD that assumes a top of a 10mm nipple - and doesn't realize that for lack of information - and uses 16mm nipples - BAM - the builder has just backed themselves into a corner where they may run out of threads before reaching the desired tension.

Furthermore, I corrected the specs for the Campagnolo hubs to that which a spoke calculator normally expects - ( --> to center-of-flange as opposed to inside of flange. ) Sure that correction is pretty minor - influence is less than .5mm.

Outside pulling spokes versus inside pulling spokes - yup - overthinking.....pick one, build it and ride.

=8-)

Since I think the OP's questions have already been answered, I hope this doesn't qualify as a thread hijack. But I have to ask, in all simplicity, what's this business about aiming points and nipple lengths? I'm not much more than a novice at wheelbuilding--have probably built 8 or 10 wheels in my life, all in the past few years--and I'd never heard of either of those things until today. I've always just plugged the hub and rim data into Spocalc, rounded down from the spoke length it gives me, and started building. The wheels have all come out fine so far.
Is nipple length a matter of physically measuring the overall length of the nipple? Are you supposed to use that number to adjust the Spocalc-generated spoke length, or what? Pretty much all of the wheels I've built have used 30-year-old spokes and nipples I bought in nearly-full boxes from a going-out-of-business bike shop. Spocalc seems to agree with them. Maybe that's just been a matter of dumb luck?
JV

This is fun. Thanks for the link OP. You guys are WAY overthinking it.


Overall we are not WAY overthinking it.

over thinking it or not i have really enjoyed everyones input. i like a good point/counterpoint thread.


Since I think the OP's questions have already been answered, I hope this doesn't qualify as a thread hijack

not a thread jack at all. this is exactly what i wanted, advice on my build and general wheel building information from the experienced builders on the forum. i vote keep the questions coming.

This is fun. Thanks for the link OP. You guys are WAY overthinking it. Get within 2mm and you're fine. After thousands of wheels - posted ERDs are just fine.

Lacing head out or head in for the trailing spoke on the DS is a personal choice and nothing more. Literally. Schraner does head in. Jobst does head out. I dare any of you to point at either one of those guys and tell them they're wrong.....because it doesn't matter which one you pick....you'll look like a fool. I have done both. It results in absolutely no difference in the end build. Pick a religion and then just stick with it.

OP - first build - no tensiometer - at 170+ in a 24/28 setup: use dt comps all around and be done with it. the revs are OK, but they are spongy and a bit more expensive - not to mention much harder for you as a consumer to find in the lenght you want for the qty you want. Most Distributors have stopped carrying Revs in their catalogs because of the small demand. Building with a rev as a first build you are going to have issues with spoke stretch and twist as it comes up to tension. Just go comps. Much better spoke, easy to build with and available in a myriad of lengths at any shop in near the whole world. Besides....if you get bored later you can just go re-lace them.

Psimet has spoken!

Psimet has spoken!

i may or may not have directed him this way via pm

Ummm...Psimet2001...

Overall we are not WAY overthinking it. ERD is very important. -)

ERD is static. Its a fixed value value that NEVER changes. If the builder happens to choose the wrong spoke/nipple combo thats the builders fault not the ERD's.

ERD is static. Its a fixed value value that NEVER changes. If the builder happens to choose the wrong spoke/nipple combo thats the builders fault not the ERD's.


ERD is not static...nor is it a standard...a whitepaper spec...etc.

ERD is:

"The distance between the end of two opposing spokes in an already built and functional bicycle wheel."

Notice, nothing in the description about the rim, nipples, threads, or joint sleeves....just the distance between the end of the opposing spokes...


However, when a wheelbuilder is trying to build that wheel NOW using existing parts - they are trying to predict the ERD of the future wheel - and have to come up with a diameter NOW.

Hopefully the "rim diameter" the wheel builder estimates turns out to be the actual "effective rim diameter" when they build the wheel...

Problem is - for the present tense - nipples size and profile, threads, and joint sleeves (if existing in the rim) all come into play.

http://www.youtube.com/watch?v=gCXFKN9JvCQ&context=C31932c8ADOEgsToPDskLaenuUwwH7Boe2oBRcEd-L

The video linked explains the effect nipple and thread behavior have on coming up with a "diameter"...and the chart at the end notes how it affects the ERD for the Mavic Open Pro 700c for example...

That chart highlights why you'll see 605.00 and 602.00 often quoted as the ERD for that rim.

=8-)

Also, when using SpokeCalc, Damon Rinard explicitly notes up front that all of the ERDs in his tab are to the top of a 10mm standard profile nipple. When using his tool - so long as you use 10mm standard profile nipples - everything will turn out fine.

Sometimes for 12mm as well - with a little luck.

Try to use 16mm nipples with the result as-is - you'll run out of threads in most case before reaching the desired tension - most 16mm standard profile nipples are restrictive. If you adjust by cutting down the spokes a millimeter or two...

...you just changed your ERD in reverse.

The spoke length calculation formula is a balanced equation - change the inputs, you changes the results. Change your results, you've changed the inputs - mostly the ERD.

=8-)

Psimet has spoken!

I particularly like the advise to dump the rev's.......

ERD's... I think when a pro works with allot of them... you get accustomed to what works. But after wading thru some of these spoke calc databases.. with name references I thought incomplete and confusing at times.. I vote always check the ERD. Can't hurt to verify.

Tension gauge. Given the OP has access to the stand.. I'll suggest a Park Tension meter.. had for around $50 now with shipping. Easy to develop a feel for how these work with good repeat-ability.. and then you KNOW what your tension is.. rather than GUESS it. I don't think you'd ever regret buying one........

SortaGrey:

"I vote always check the ERD. Can't hurt to verify."

Absolutely, hence my recommendation early on...

Gotten burned by Velocity once...the DeepV did change awhile back...and KinLin once with the ADHN...they changed the 26" a few years ago...

...worst offender is Weinmann....with that Trak Attack rim. Damn thing floats between 556 and 560 when aiming for the flat of a 12mm nipple....can't stand the damn things...

=8-)

Weinmann were never my favorite brand of rims anyway. Forget them.

For the ignorant among us, how do you determine the nipple length? Could it be as simple as measuring the overall length with a metric ruler? Or is it something more than that?

I particularly like the advise to dump the rev's.......

why is that? he is not the first person to suggest using all comps for a "first timer"

why is that? he is not the first person to suggest using all comps for a "first timer"

Comps are more stable, for lack of a better word, as the tensions get higher.

Comps are more stable, for lack of a better word, as the tensions get higher.

i understand that but SortaGrey sounded SortaSarcastic with that statement. i may have read in wrong though.

ERD is not static...nor is it a standard...a whitepaper spec...etc.


I'm looking at a rim next to me and unless the laws of physics change I'm trying to figure out how its going to shrink (reduction in ERD) or enlarge (increase in ERD).

I'm looking at a rim next to me and unless the laws of physics change I'm trying to figure out how its going to shrink (reduction in ERD) or enlarge (increase in ERD).

Estimating what an ERD will be for a wheel involves determining the physical seat or nipple bed diameter of the rim [[PLUS]] modifications for nipple thickness, thread behavior, etc., all of which is left to the judgement of the wheel builder.

You are fixating on the physical rim AS-IS - that is NOT ERD.


As I already noted for you, ERD is:


"The distance between the end of two opposing spokes in an already built and functional bicycle wheel."


Where the ends of the spokes end up is driven by the wheel builder and the parts they are working with.

=8-)

For the ignorant among us, how do you determine the nipple length? Could it be as simple as measuring the overall length with a metric ruler? Or is it something more than that?

Just squeeze the very top and the barrel end of the nipple between a caliper.

For standard profile nipples in 15g and 14g you'll see:

10mm
12mm
14mm
16mm
20mm

Watch out though, there are something called low profile nipples out there. In my video linked earlier, I show an Echelon 10mm low profile nipple. Behaves similar to a standard 10mm nipple - but you wouldn't want to use 'em with single wall rims.

When you get to 2.6mm or 105g spokes, the nipple sizes are typically 13mm and 16mm, although I have seen 10mm.

=8-)