SO I have this Monarck road bike. A standard size quill stem is too large to fit. I tried several. The digital calipers says the inner diameter of the steerer is approx 21.7mm. What would this translate to for a common size for a vintage quill stem? Thank you.

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MCB builds with a 25.4 steerer so one would expect a stem size of 22.2

wonder if your measurement may be due to deformation

verify that opening in locknut not smaller than opening in steerer

have never heard of them employing .833 for example

should you have an .833 stem in your parts bins you could give it a test fit...

you need to hear from our styggno1


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Did you install the HS? The stack looks tall was there any work done to the fork? Longer steerer maybe?

If it's a standard 1" HS employing 32mm wrench I agree it should be a regular 22.2 quill

I put that headset on, but even if the steerer is any longer, that doesn't make it any narrower. So that is irrelevant. It's a standard generic 1 inch headset, 32mm. The fork steerer appears round and undamaged.

Jicafold I was wondering if maybe a cheaper steerer had been used for a donor and therefore a narrower inside diameter.

Did you try removing the locknut and wedge and trying to insert the quill?

21.7mm stem.. they exist... and they are mostly old. i hhave two bins of gooseneck stems here...One of the 21.7mm is an old Sakae Ringyo, SR brand, and all aluminum.. the others are steel or BMX steel with an aluminum BMX style clamp...
i have some that are 21.7mm.. and more that are 21mm, or slightly under... one of the 21.7mm stems is an ancient Antique Cast Iron beauty that weighs around two pounds.
i think older Peugeots used an undersize stem at times... those were Pivo brand, IIRC, but might be a 22mm instead of a 22.2mm, which is the most common size for a 1" threaded steerer fork.

the 21.7mm size would be found in old style, lower grade steel forks that needed the extra-thick tube for safety.. newer alloys and tube mfg. tech. were much stronger. and could be made with thinner walls.
BMX people can bend ANYTHING, so they went with the thicker wall tubes... I've worked on cheap steel BMX bikes that weigh more than my old drum brake Tandem does... the BMX bikes still get bent up.

Schwinn used a 21.1mm Stem... talkin' about Old, Chicago Schwinns, not the new taiwan ones...

No. I should try that. Good idea.

Well, that did not work either.

what WILL Work is getting a 21.7mm stem.

FYI: I have a 1974 Crescent Pepita 92319. It’s stem measures 22.1mm just above the top nut. I’m not certain that this matters but there were many commonalities between the two lines.

From where? There are none on Ebay.

Jicafold, the stems from Origin8 are smaller in diameter than most. I've used them in French steerers and only once did I have to sand it down a bit...using 220 grit and a shoeshine style sanding for < 5 minutes.

Thank you. That's what I was thinking of doing something similar to that to take a little bit of metal off and make it fit. I'm glad to see that worked for you. "Making it fit" has generally worked in other aspects of my life over the years....why not here?

Do you mean 21.15mm? Sometimes these are labeled 0.833". Are you sure there are 21.7mm stems?

well, either there are, or my rather spendy mitutoyo digital calipers are broken. i just used them a few minutes ago... seem to be in excellent working order.

i also noted that i'd measured several 21.1mm stems too...

and i could have brought out my Micrometers to REALLY get a close reading....
and i was trained in Machine Shop Tech (4.0 graduate) when i was a young teen.. so... Yep... 21.7mm it is.

the "21.1mm" stems trend towards 21mm or slightly under, IIRC. old school and low school... one of the "21.1s" is still wearing the chromed schwinn shifters...

i could have gone into the hundredths of mm, and recorded each one, but i simply don't care or need to.

and you could find a Co-Op with a stash of the Pivo French stems around... they trend a bit undersized... and one of the 21.7s here is an old, beat up Pivo stem... many older UO-8 Peugeots used them...

heck... hit up a Peugeot Owners forum on Facebook ... they might have some...
unfortunately, this site doesn't let me sell you one. and that SR stem is a crazy short reach, anyway. like, 35 or 40mm, as a guess... !
i just re-measured it... 21.71mm stem... no signs of sanding or filing on it.

seriously... hit up a bike pack rat or Co-Op near you... look at the french bikes' stems..

sanding off a half Millimeter (.020") will take several hours to do well.... a French 22mm stem would be a MUCH better starting point, i'd think.
they are on Ebay, frequently, if not right now...

PS.. aluminum dust is kinda toxic,,,, too much will cause flu-like symptoms... been there, had that... 105*f temp. and the WORST runs ever... for a week.... !!! so wear a mask, and gloves, ok?

well.. look what i found ... go search... "Vintage Bicycle Stem French Spear Point AVA style New Old Stock for Road Bike"
on Ebay,,,, guess what ... 21.7mm, as witnessed on the seller's caliper... kinda cool looking too!

seller description... "Vintage Bicycle French AVA style Spear Point stem for road bike NOS. New Old Stock, brand new, never installed. Please look at the photos. The diameter measures just less than 7/8" or just under 22 millimeters. It's about 7" tall and has a 5.5" reach. Will fit handlebars with a 25.4mm center diameter (see photos). Great looking and will look awesome on your vintage road bike!"

It is possible that the butted steerer tube was installed upside down so that the thicker-walled section is at the top rather than in the fork crown where it's supposed to be.
Brent

Thank you. That was too good to pass up. I bought one.

The Threads are rolled or cut on the tubes Before the steerer tubes are brazed or welded to the forks/crowns.
the Threading process is done in a lathe to allow higher precision, and speed of process.

Yes; and since the steerer tube is of a uniform outside diameter (if we discount the modern tapered steerer tubes) those threads can be rolled on the wrong end.
Brent

ok... so how would that fork be fitted with the same gooseneck as all the other bikes being assembled before it leaves the factory?

maddog

and that wasn't the only 21.7mm gooseneck i've found online.. the other two on Ebay looked terrible, IMO. A NOS with a REALLY SHORT extension, and a dinged up and scratched mess Pivo brand.
and then, there's the Short extension SR in my stock here. and a Pivo with a nick in the short Extension.... etc.
pretty sure i've run into the Monark 21.7mm stem issue before, but it's been DECADES, in that case... i owned one, briefly, WAY Back When.

what you're doing is trying to say Carrier Pigeons never existed, because they're extinct now.
hey, suit yourself, i guess.

the 21.7 size was so close to the 22.0 size that most get them mixed up, and blame their poor measuring tools...
Peugeot and Monark have both used that size.... and i'd think that Gitane may have too....
the search i used was "French Goosenecks Stems"
good ones at fair prices come and go quickly on Ebay. A few days ago, only that trashed Pivo was up.