This is a term in climbing for
having very strong fingers
The posession of fingers of steel allows one to hold
onto the most malicious crimper
Other powers that they invest upon the owner can include
(but are not limited to) being able to
preform one finger chin-ups.
Ben Moon was giving a lecture about his climbing
exploits and mentioned that one really needed
to be able to do push ups on ones little fingers.
A member of the audience retorted that this was bollox
so Ben Moon promptly dropped to the floor
and demonstrated that he did have fingers of steel.