recessed headless recessed hex setscrews

[Mark Kinsler]

Recessed headless hex setscrews (aka 'Allen' screws in the US) can do one 
other nifty trick: they can split.  It feels just like the internal hex has 
rounded out, but an 'easy-out' won't grab the screw.  Since the screws are 
hardened, you can't drill them out.  Application of a screwdriver won't 
help, either: the sharp-edged pieces of the screw just dig into the threads.

This phenomenon seems to be rare, fortunately.  It happened to me on an 
aluminum knob.  The fool knob was the only obstacle to removing the front 
panel of a tape recorder I was repairing.  I finally, laboriously, hacksawed 
the %$#@ knob off and replaced all of them with a set that seemed plausible.

I also learned, fortunately through a good teacher, that sometimes there 
will be _two_ headless-hex setscrews in one hole; one on top of the other.  
The idea is that one screw locks down the other.  It can drive you crazy if 
you don't suspect it.

M Kinsler

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