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Tapping shifter boss threads(7 posts)

Tapping shifter boss threadstrout_bum
Mar 20, 2003 9:21 PM
I've decided to put STI levers on my bike. But threads on right side boss are not cut deep enough to mount cable stopper. I'm using a thick washer just to get everything set up, but I think I should have a little more bite on screw. Is it fairly standard for shops to have the correct tap size to do this? The threads are cut about 1/4" deep and then it's smooth. What is the standard thread size/tap size for shifter boss screws?
It's the same as a water bottle cage bolt.Spoke Wrench
Mar 21, 2003 5:17 AM
I'd think any decently equipped shop would have the correct size tap.
5mm x 0.8mmCalvin
Mar 21, 2003 5:36 AM
The tap would be a 5 x 0.8mm thread. Use a "bottom" tap, which is better for tapping blind holes, such as those in your mount.

You should consider having a good shop look at this. Cutting new threads down inside the mount would may prove fairly difficult. If you have adequate threads now, you may want to just shorten the washer.

The tap below has a long lead, which helps guide it straight. It is not a bottom tap, which has a much shorten lead at the tip. This allows it to cut more threads.
5mm x 0.8mmnelson
Mar 21, 2003 6:58 AM
Be very careful, I've seen more than one frame ruined by puncturing the downtube with a tap when cleaning out these threads.
re: Tapping shifter boss threadsRusty Coggs
Mar 21, 2003 7:23 AM
Why would you need more than 1/4" of threads on a cable stop? The cable stops fit snugly over the bosses and prevent movement,and the screws just keep then from falling off.Wasn't there enough there for downtube shifters.Use teflon tape or non permanent loctite on the screw threads and don't overtighten as is such commmon practice.
what makes them "not deep enough"?C-40
Mar 21, 2003 9:35 AM
If you have 4 turns of engagement, that's enough. If the mounting bolt bottoms out, then cut off a couple of threads.
what makes them "not deep enough"?trout_bum
Mar 21, 2003 11:01 AM
There is enough thread engagement-my downtube shifters mounted up fine. I think I will just try to get a shorter mounting screw - M5 x 8mm long should work-or if not cut one down a bit as you said.
Thanks for the help.