I want to move from 4.5mm threads on my Ross Signature shifter bosses to 5mm so i have more choice of shifters. To do this do I need to get a specific size of 5mm tap or just ask for one for M4 5mm?? Just wanted to be sure because once they are tapped I can't go back....

First- There is no M4 5mm. M4 is a 4mm OD.

Second- do check the boss's shape and it's compatibility with other shift levers.

Third- A bottoming tap will tap to nearly the base of a blind hole, which is what a boss has. Generally one uses a tapered tap then a plug tap and then the bottoming one.

Do be careful with the tap contacting the bottom of the hole. Tap breakage is very easy. Andy

Does M4.5 have the same pitch as M5? If not, when you try to drill and tap M5 where the M4.5 hole is, you will probably end up with a mess - there's not enough difference that the drill will clean out the M4.5 threads completely. If they are both coarse thread they are both .5mm pitch.

How does the thread size effect the shifter?
No goin back if you tap it.
Keep it simple try a washer first.

Andy

I understand I will have to very carefully file tabs on the bosses to allow the replacement bases to fit.

Was going to drill a pilot hole first through bosses into frame (figure the base of each boss will cover those) and then wanted to tap the bolt holes to allow use of the slightly fatter bolts that rest of my shifter choices have. If I predrill the bosses the tap shouldn't bottom out.

Does this make sense??

Sorry the current shifter bolts are a slightly smaller diameter and thought they were 4.5mm but are they infact M4.5 bolts??

...if there are screws currently installed on this frame in the shifter bosses, you would do well to take them to some industrial fasteners place and get them measured. I,too, am unfamiliar with M4.5. I suspect there's something wrong here, but I can't exactly understand what it is.

Anyway, I'd hate for you to come to grief over this. If all else fails, just buy and M4 and an M5 machine screw at the Home Depot and use them as gauges for what you have now.

Yep, do the math: https://www.engineersedge.com/hardwa...ead-sizes1.htm

No, the most common 5 mm bolt is M5x0.8 and is the coarse pitch. M5x0.5 is the fine pitch and rarely found on bicycle components.

Thanks. Yes, my bad. In M4.5, coarse is .75 I believe. I like to believe things on modern bikes are standardized well enough that I don't have to think too hard about metric threads.

I'd like to believe in world peace too but reality says otherwise. The bike business if full of mixed dimensional (metric and fractional) and designs meant to further the manufacture's profits and not the end user lives easier. Andy

Campagnolo type bosses are 5mm x 0.8mm thread; some Shimano bosses are 4.5mm x 0.75mm thread. I doubt you could retap a 4.75 x 0.75 boss to 5 x 0.8 without problems. Shimano did make a conversion kit to mount Campagnolo type levers ona Shimano "A-type" boss:


Source: Sutherland's 4th Edition

Hmmmm.
I've actually had good luck tapping a 4.5mm bolt hole (old Shimano style) to 5mm X 8 using either a 'poor man's tap' - essentially a hardened 5mm bolt with a pair of vertical valleys Dremeled into it- or a 5mm bottoming tap so that it would accept a now-standard 5mm mounting bolt for a cable stop or downtube shifter.

Just be careful and take your time. No need to drill anything out, just re-tap the threads.

[MENTION=170517]rccardr[/MENTION] - I think it was your thread that got me thinking I could do this!
Modification: Old style Shimano downtube shifter mounts to later style

I was going to drill through into the down tube first with a very fine bit to prevent having the tap bottoming and breaking. I get that I have to stop after every 1/4 turn, reverse and clean the threads and that I must oil the tap.

Do I not still have to very carefully file tabs on the bosses to allow the replacement bases to fit?? Or, are you saying that just re-tapping the threads will be all I need?

I saw the mention of using the .5 inch hole saw and thought if I did this after drilling it my be neater and have a more flush fit to the frame
https://www.homedepot.com/p/Milwauke...0511/204994403

The Ross currently has the Shimano Z401 shifters and I wanted to switch to Exage Sport Shifters, if only because I have the same model levers, FD and RD on the bike already.

Why not keep the existing screws we all know work & swap the lever?

These are downtube shifters, correct? What am I missing?

Not really.

Of course, you might be able to use the 4.5mm bolts with a small washer to hold the larger shifters. That would be ideal - no machining.

If that won't work what does the current setup look like? Pictures with the current bosses mounted and (if they're removeable) with them removed would be useful.

I am familiar with two scenarios. One is that there are bosses welded in place and you want to enlarge the thread from M4.5 (4.5mm od x 0.75mm per thread) to M5 (5mm od x 0.8mm per thread). If so, you don't need to drill holes in the frame. There exist things called bottoming taps. Ideally you use these in association with two other taps. The first one is more tapered and gets you started, but doesn't thread all the way down. The bottoming tap has almost no taper and taps almost to the bottom of the hole. There's a tap type that is midway between the two that you use in-between the taper tap and the bottoming tap.

If the current setup has a stud from one side to the other that holds the bosses, and the whole assembly comes off, then just enlarge the frame hole a bit and swap out a new set of bosses, which should be available for your frame size.

If you are planning on drilling into a modern, high strength frame and then tapping the frame, it won't work. Not anything I'd try, anyway. The alloy or steel is very strong and so is used in very thin wall sections so its too thin to hold threads. There are techniques (you drill a very small hole then indent a little nipple into the metal, and then thread the nipple). The pic below shows the ideal case of holes that are extruded and could be effectively tapped. Hard to do perfectly in a closed frame like a bike tube.

BTW, I can envision no scenario where I'd want to use a carbide grit hole so on anything remotely related to a a bicycle frame or part. That type of tool is for drilling very rough holes in ceramics. There are carbide-tipped hole saws that you might use on, say, work-hardened Reynolds 953 but that would be shop use in fabricating frames, not bike mode work. What was your intention? How are you proposing to use this?

I suspect [MENTION=466491]WGB[/MENTION] meant to drill into the tube through the boss, so he could use a standard plug tap to re-thread the boss rather than searching for a bottoming tap. But your point about drilling modern, heat-treated alloys is valid. Depending on the specific frame material, it might be a bit of a chore.

Measure.. there are thread pitch gages , which are part of most machinists tool boxes...

Metric pitch is thread per MM , so count how many per 10mm then divide by 10 .

I had this update fully typed then had a power failure!

Starting again.

First I'd like to apologize because I didn't post any pictures.

Here is the shifter boss for my Ross Signature. Current shifters are Shimano Z401. These take a Shimano only proprietary bolt (machine screw?? lever Screw??). I recently acquired a partial Exage Sport groupset which included the shifter set but no bolts. I reached for some spare bolts and no, standard M5 shifter bolts don't work because the Z401 bosses are threaded for a smaller bolt size. I believe that the current bosses are Shimano A type bosses and require bolts that are referred to variously as M4.5 x .75 or 4.5mm x .75. They are ones referred to by JohnDThompson above.



Z401 and Exage Sport shifters



Exage on top and 401 on bottom


The original bolts are a MM or so too short to fit through the Sport shifters and engage the threads of the boss and the Exage require a different boss cover than the Z401 have.



401 base on top and Exage on bottom

I spoke with a local frame builder who suggested that rather than search for longer M4.5 bolts I should just tap the threads to take the M5 x .80 bolts. I would have had him tap it there and then but I didn't have the frame with me. He walked me through the tap process and it seemed straight forward.

I approached a neighbor who has lots of taps and other nice tools but he didn't have any 5mm taps. The neighbor suggested that I insert a drill bit into the bolt hole in the boss and drill into the frame and he said that drilling would prevent the tap from bottoming out and breaking in the threads (at least I think that's what he meant). Judging from the response on here, I guess that pre-drilling before tapping is not needed.

The neighbor suggested a local store to get the tap. I began to wonder if there waa certain thread size that I needed and now realize the .80 part of the M5 x .80 will cover that question.

This brings me to the next part where my post was confusing

The replacement boss covers won't fit onto the bosses and so the bosses must be modified or trimmed to allow the mounting of the new bosses. In his post RCCARDR used a file very judiciously and trimmed the stop so that new covers would work.

RCCARDR photo



As for the drill comment, I found a thread on here where someone taped the frame to prevent damage and used a 1/2 inch hole saw with a 9mm center to very carefully trim the boss to allow the boss covers to fit snugly to the down tube. I suspect I could get by with just the tapping of the threads and a little - very little - filing.

Modification: Old style Shimano downtube shifter mounts to later style

brewerkz photo before




brewerkz during photo



brewerkz after photo

Unless the mfr is really cruel and wants to screw with the customer by not using metric standards, you likely don't have to measure. M5 course is 0.8mm pitch and M4.5 course is 0.75. But I agree with CyclingFool that if you just stuck an M5 tap into the thing, you might end up with a mess.

To throw another idea into the mix, if you are drilling a through-hole anyway, you might use a form tap rather than a cutting tap. The cutting tap would cut new grooves that may interlap with the old threads, and the interaction might tend to cause the tap to go in at the wrong angle. If that happens, the tap will likely break. Also, a cutting tap will remove metal without regards to whether that material is needed. A form tap will move the metal around. I think you'd get a better thread with a form tap.

That said, I'm pretty sure that this fastener is not super high stress (may be wrong- has anyone ever pulled one out or broken this type of screw in use?)

You're missing that there are different and obsolete DT bosses out there that are not compatible with newer shifters.

Ah! Ok. I learn something new every day.