Originally Posted by
100bikes
One simple trick is to put a deflated balloon over the end of the allen key and insert it into the hole.
Sounds a bit silly, but it can work.
Vibra-Tite Drive-Grip
https://www.vibra-tite.com/specialty...ite-drivegrip/ or Liqui-Moly Screw Grip
https://products.liqui-moly.com/screw-grip.html (likely the same thing) may also work.