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Discussion Starter · #1 ·
I'm trying to change my downtube shifter mounts to M5 from M4.5. I've looked for a M5 tap as a "short-projection", "pipe", "conduit" and a "straight flute" and nothing I'm finding has either a shallow enough tap or I can't find it as M5.

Any ideas on how to tap this? I sadly don't have access to a lathe.
 

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Discussion Starter · #3 ·
I think the M4.5 pitch is .75, so maybe a M5 .8. I'm honestly worried about the pitch, I've never tapped up .5mm so I'm not sure if there is going to be enough to bite with an M5 at any pitch.

Adding the word "bottom" or "bottoming" was very helpful, thank you :).
 

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M5 x 0.8. You may have to drill a pilot hole first as going straight to the M5 tap may be too much and crack the tap or the braze-on. You will have to start with a TAPERED tap. Obviously, you don't want to drill or tap into the downtube. Follow up with a PLUG tap. Finish with a BOTTOMING tap.

Are you sure the O.D. is correct for the new shifters before you begin?
 

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Discussion Starter · #5 ·
This mount is actually a little thing that mounts to the high side of the downtube, I don't know it's name. So, I might drill a pilot all the way through :-/. Once the levers have been removed, I'm not sure there is enough wall thickness for anything but a M5 .08 as any greater O.D. would seemingly be a "close call". And no, I'm not yet sure of the O.D. for these little dura ace shifters but they have "M5" stamped on... but of course I still have to check.

The M5 tap won't be here until Monday, so I have the weekend to think over my future mistakes. FWIW, M4.5 is a pain in the ass because nothing but M4.5 seems to really go in. I would of forced a imperial threading in or a proper M5 but that .5mm difference makes things too indeterminate to attempt typical brute force approaches.

1984 Univega Gran Rally with high side shifter - mounting holes M4.5 (If only I could find a M5 version of it... but no luck).
Hood Bicycle tire Gesture Bumper Automotive tire
 

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Discussion Starter · #6 ·
Sorry to double tap, but what makes the shifting levers shift? Is it the tension between the silver piece and the lever, or is it what's under the outter black addition on the lever?

I ask because I could 3D print a small little cast and make an aluminum adapter and/or mount... but I'm not sure how the "click"/shift happens.
 
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