Phil, Squid-in-Training wrote:
I would say extra long allen wrenches (2.5mm - 6mm) are a recipe for a
twisted wrench... bolts those sizes never yield, and 8-10mm wrenches
torque down no problem.


Never yield? Never's a long time. I've seen plenty break, right at the
base of the head. And not *all* my fault. :-)
Usually though, what I've seen is that either the bolt head or the wrench
strips. Maybe it's the bolt/wrench tolerance, but to me it seems like 5mm
bolts can snap or strip easily, but 8 mm can handle more torque than I can
give. Go figger.


It's the effective force at each facet of the wrench. If you give 1Nm of
torque on a 1m wrench, the flats of a 5mm wrench will experience a little
less than 200N at the wrench/bolt interface, whereas the flats of a 8mm
wrench will experience only a little less than 125N. That's a reduction of
almost 40% with only a 3mm size difference.

That 'splains it then, thanks.

I've broken cheap 5s that consist of metal bonded together with a seam
running down the middle... a poor excuse for a real tool. Forged tools are
the only way to go.

What kinds of bolt heads have you snapped, and on what specific part?

Brake cable binder bolts (SunTour road as well as cheapy ones in the
shops I've worked in).

Shawn