Bicycle Mechanics - Worn out hex screw!

I was trying to install new thumbies for my gear shifters but the hex screw on my right grip shifter won't come off! I think it is worn out, because the left one came off just fine. It still retains its shape, though. I tried the next biggest size and that won't fit at all. Any suggestion on how to remove a tightly screwed hex that has a worn out head? Thanks!

So it sounds as if the hex hole is rounded out. You could try an "american"-measurement hex wrench set, to see if there's one slightly bigger than the metric one, that'll fit in the enlarged hole. But I think this is unlikely anyway. If you can get anything to work with hex wrenches, it'll probably have to involve
(a) soaking the threads in question in WD-40 or liquid wrench
(b) very careful turning of the wrench while pressing the wrench head full-force into the bolt - think of a phillips screw that you're worried about stripping

If this doesn't work, best thing to do is use a power tool to drill a flat groove into the hex bolt head, so you can use a flathead screwdriver on it. This method is sometimes used with hex bolts on SPD-style cleats, where the surface has worn down and a hex wrench is no longer usable to loosen the cleats.

I was trying to install new thumbies for my gear shifters but the hex screw on my right grip shifter won't come off! I think it is worn out, because the left one came off just fine. It still retains its shape, though. I tried the next biggest size and that won't fit at all. Any suggestion on how to remove a tightly screwed hex that has a worn out head? Thanks!

Try a brand new allen wrench. That'll work more often than you'd think.

If all else fails could the bolt be removed by first using a drill of slightly smaller diameter than the original hole to drill out most of the bolt, using a slightly undersized tap to chase out the fragments, then a correct tap to re-chase the threads? Any machinists to advise on this?

Try a brand new allen wrench. That'll work more often than you'd think.

That's very good advice. Here's more...if you have access to a bench grinder, you can make a worn out Allen wrench new again by grinding a couple of millimeters off the end. Don't overheat it though...stop to quench it in water every time it starts to get hot. If it changes color, you've cooked it.

Sheldon "Sparky" Brown

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Screw extractors ("easy outs") are always an option, if all else fails. Unfortunately, they are hardly ever "easy" to use. But, they do work.

Another option is to use some JB Weld (available at any auto store and some X-marts), and expoxy the wrench to the bolt. Allow it to dry solid and just unscrew the bolt. Just be careful not to get any on any other parts! You can then cut the wrench off where it was expoxyed, and still have use of the hex wrench, it will just be a bit shorter.