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Old 09-01-08, 01:12 AM   #1
SpinUp
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Non-standard metric threads

I've got an old Peugeot that I'm trying to put new shifters on, but the threads of the braze-ons are M5x1.0 instead of M5x0.8. I can't seem to get any screws with this thread pitch, so what's my best option?

If I tap, can I tap to M5x0.8, or do I have to go to M6? I don't have any experience with tapping threads. Thanks for any advice.
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Old 09-01-08, 06:23 AM   #2
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Check with some of the on-line or brick and mortar Fasterner Supply or Industrial Supply shops (Grainger, McMaster-Carr, etc.). They often have fasteners in unusual diameters and thread pitch.
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Old 09-01-08, 07:49 AM   #3
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If you tap with a M5x.08 you are running the risk of the screws pulling out since there won't be much left for the screw threads to grab onto. If you are going to drill them out some more anyway, try it and get some blue loctite for a little extra insurance.

I think a better plan would be to put an M5x0.8 helicoil in there. These come in kits and it will tell you which size of drill bit to use, it might be a metric bit, or maybe a fractional or number bit, you'll have to check.

I've got an older French Zefal Husky floor pump that has fine metric threads on the hose. Recently I got a Topeak replacement hose with an adapter kit that claimed to be suitable for Zefal. Not this zefal apparently. I'd llke to be able to find the appropriate threaded brass pump fitting to work with this new hose.
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Old 09-01-08, 09:07 AM   #4
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Don't tap M5x0.8, you will not have enough metal left for the screw to hold because of the different thread pitch. Your best bet would be to drill 5.0 mm (or drill bit #9) and tap M6x1.0 (if there is engouh material to do that).
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Old 09-01-08, 10:23 AM   #5
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First of all I'll reinforce the others in saying do NOT just try to retap it with a 5 x 0.8. The threads WILL be ruined and the holding power will be minimal.

Another option to add to those above would be to drill and tap for 5 x 0.8 helicoils.

But drilling down and tapping blind holes of that size is not for the unpractised. Regardless of if you try for the 6mm or go with the Helicoil idea practice first with a tap on some scrap metal. Close isn't close enough for stuff like this. You want to get it right and there's seldom any second chance on shallow blind holes.

Assuming the mounts are blind holes ( blind = doesn't go right through the tube) and you tap for 6mm or for a Helicoil then you'll need a bottoming tap AND a mid taper tap. Starting a bottoming tap is a pain if you don't do it with a machine to guide the tap for the first couple of threads. The mid taper will start the thread much easier but once it hits bottom (don't force it, feel for the sudden increase in back presssure) you then pull out the mid taper and flush out the chips and then run the bottoming tap in.

This is a lot to remember for someone that's never threaded anything. If your head is swimming then take it to someone with the right stuff and give them money or beer to do it for you. Or find the oddball screws you need.
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Old 09-01-08, 10:47 AM   #6
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What kind of shifters are you planning to mount? If they are STI (aka brifters) or bar-ends and all you need to do is fasten the cable stops over the current downtube bosses, I may have a solution for you.

If you want to upgrade current downtube shifters to newer downtube shifters, disregard the above.
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Old 09-01-08, 03:17 PM   #7
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Unless Peugeot manufactured their own taps, there's no such thing as a 5mm x 1.0mm thread. 5 x 0.8mm is much more common but a 5 x 0.9mm also exists (though I've never seen it used). How did you measure the thread pitch? Have you tried a standard M5 screw to see if it fits?
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Old 09-01-08, 03:42 PM   #8
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Did Peugeot ever use imperial sizes? And if so when did the switch take place? I'm wondering if it's actually a 10-32 size.

It can be hard to measure internal threads on small holes so I'm guessing that he guessed....

Ya know... it may even be that someone forced a different screw in there at some point and messed things up for you. Can you try to look in there with a magnifier and light and see if the threads look clean and crisp or are they chewed up?
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Old 09-01-08, 04:55 PM   #9
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The other M5 thread is M5 x.75mm which is close but no cigar to M5x.8mm. I wonder if that's what the OP has. I've never seen an M5 x 1.0 either.
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Old 09-01-08, 11:20 PM   #10
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Thanks for all the replies and info - especially about the different kinds of taps to do the job, and the helicoil inserts. Given the pictures below, does it look like there's enough material there to do the job?

I'll probably wind up calling around to a few shops and see if I can get them to do one of those options for less than the cost of the tools to me. I've still got a few emails out to specialty fastener places, but I'm not optimistic - as is reflected in the posts here, no one has heard of an M5x1.0 thread.

Just to clear a few things up - I am in fact replacing the downtube shifters, and not going to brifters. The hole is not quite a blind hole, since the threaded piece sits on a small tab, but the through hole is a smaller diameter, so I may have to treat it as a blind hole in practice.

How I determined the thread pitch: I did of course try an M5x0.8 screw and it wouldn't thread in past one turn. I have the original (ugly, plastic, friction) shifters that went on this bike - and the original screws, which thread in very smoothly. On visual inspection, the threads on the old screws are noticeably courser than a standard M5. The screws are also too short to be used with the new shifters.

I took the old screw to a hardware store with a display board including all the various sizes of standard and metric screws and nuts. After trying the screw in all the nuts (including 10-24 and 10-32) to no avail, but confirming that the diameter was 5 mm, I held the screw threads up against the studs on the board. The screw was a thread-for-thread match to both the M6x1.00 and M7x1.00 screws - perfect. Therefore, M5x1.00 - it exists!

A crazy idea just occurred to me - what about welding or soldering the old screw without its head onto a new M5 to extend the length? I only really need the threads on the bottom. Is there any chance it would be strong enough?




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Old 09-01-08, 11:27 PM   #11
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I've run across a couple old bikes like that. In most cases, I just drilled through the tubing and tapped for M6 bolt. In some cases with a nicer frame that I wanted to repaint anyway, I just removed the bosses and brazed on new ones (the base of the original boss was too tall and wouldn't let the concave washers for newer shifters mate up with the frame completely).
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Old 09-02-08, 07:23 AM   #12
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Well, you really did your homework!

From your photos, the current bosses don't look like normal Shimano/Campy/Sun Tour style downtube bosses either so, even if you can find the right bolts, the new shifters may not fit. Try-fit them first before putting any effort into rethreading the old bosses.

New braze-on bosses may be your only choice if you want to use more modern downtube shifters. As I mentioned above, if you are willing to fit brifters (expensive) or bar-end shifters (much less expensive) there is a way around this problem.
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Old 09-02-08, 09:43 AM   #13
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How do I know what the thread pitch is? I did of course try an M5x0.8 screw and it wouldn't thread in past one turn. I have the original (ugly, plastic, friction) shifters that went on this bike - and the original screws, which thread in very smoothly. On visual inspection, the threads on the old screws are noticeably courser than a standard M5. The screws are also too short to be used with the new shifters.
You use a thread pitch gauge. It's got a bunch of blades with thread spacings cut on them. You stick it to the side of your fastener, and find the one that matches your threads. Since there's no such thing as M5X1 threads, I'd bet you've got a #1 BA thread. That's 5.3 mm in major diameter, with a thread pitch of 0.9 mm. If it's got a hex head, your fastener should then have a 9.275 mm across flats measurement. (actually a touch less, that's the wrench size). Might also be a 3/16 CEI thread. :wq
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Old 09-02-08, 11:30 AM   #14
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That's an early seventies Peugeot. You'll find other oddball threads on that bike. I think you'll find that nothing but early Simplex shifters will fit that boss. The later Simplex Retrofrictions don't fit, either. I have a '74 PA10 with the same boss. I converted it to a fixed gear and force fitted a bell on the boss.
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Old 09-02-08, 11:31 AM   #15
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Thanks for your advice, dscheidt, but I wasn't really asking the question there, I was answering the naysayers to prove how I determined the thread pitch (see the paragraph below the one you quoted). I suppose my bold text should have been 'How I determined the thread pitch:' - I've changed it now.

As an extra bit of support, note that these threads are on a French bike from before 1974 - every dimension except the freewheel and pedal threads are metric. The dimension across the flats of the hex head on the screw is 8mm, or maybe just a bit less - it takes an 8 mm wrench.

At least the sizes of the square base and round boss haven't changed in 40 years - the new shifters fit perfectly (except that they don't quite meet the frame as DannoXYZ noted.)

Last edited by SpinUp; 09-02-08 at 11:38 AM.
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Old 09-02-08, 11:44 AM   #16
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The bottom bracket and fork threads are also non-standard French. Simplex Super Competition Shifters will also fit that boss. The levers are aluminum, but they have plastic wing nuts that always break. The boss for the left side is part of the special clamp you must use for that frame.
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Old 09-29-08, 09:27 PM   #17
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I would definitely recommend to any other newbies in this situation to go with the helicoil inserts. The drilling, tapping, and insertion of the insert was quite easy thanks to the advice in this thread.
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Old 09-29-08, 11:01 PM   #18
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I would be hesitant to say a thread does not exist. I have seen some pretty odd combinations.
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Old 09-29-08, 11:49 PM   #19
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Drilling to M6 could be problematic. Get an M6 and see if it fits through the new shifter.

M5x1.0 is is rare but it exists. If it's a shoulder bolt it will be even harder to find. Might consider having a machinist make you one (or two).
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Old 09-30-08, 01:26 AM   #20
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I would definitely recommend to any other newbies in this situation to go with the helicoil inserts. The drilling, tapping, and insertion of the insert was quite easy thanks to the advice in this thread.
WELL DONE! For someone new to this sort of thing it can be a daunting task when looking at the tap and the coils and knowing that it needs to be quite carefully done.

The taps are a longer taper on the nose. Did you drill right through the tube so it could cut the threads properley? Some might shudder at the idea but I don't think it's a big deal if you did since the brazed on mounts strengthen the tube there anyway. Or did you manage to find a bottoming tap? Or did you grind the kit's tap down to a bottoming tap shape? Just wondering.
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Old 09-30-08, 12:08 PM   #21
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5mm x 1.0 machine screws are available along with the matching tap and dies. Glad you got it fixed anyway.
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Old 09-30-08, 12:18 PM   #22
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I have a variety of taps, dies and thread counting gauges, I'll measure one of my old Peugeots when I get home.

Personaly, I'd take whatever advice Dirtdrop has to offer on this topic.
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Old 10-01-08, 12:18 PM   #23
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The taps are a longer taper on the nose. Did you drill right through the tube so it could cut the threads properley? Some might shudder at the idea but I don't think it's a big deal if you did since the brazed on mounts strengthen the tube there anyway. Or did you manage to find a bottoming tap? Or did you grind the kit's tap down to a bottoming tap shape? Just wondering.
I was considering grinding off the end of the tap, since there's a long section of taper as you say. There is some space between the braze-on bracket and the frame, however, so that helped the cutting parts get closer to the bottom of the hole, and it seems to have been enough. The very pointy end of the tap left a mark in the frame tube, so it may have been a better idea to dull that first.

In practice the new threads formed by the insert work perfectly and feel very solid. Also I forgot to mention that I keep an eye-dropper bottle of mineral oil around for lubing spoke nipples, so that came in handy for keeping the tap cutting smoothly.
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Old 10-01-08, 01:10 PM   #24
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shew-- get a drill -- go all the way through to the other side-- long stainless and a lock nut-----
no bigger than the existing hole--- ya- I know --- just forget the whole thing-- get a clamp on.
or.................... single speed it...... now that I have offended everybody with my lack of wisdom-- I will drink now......................................
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Old 10-01-08, 03:25 PM   #25
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get a clamp on.
qft
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