Brown & Sharpe #2 Universal Mill
501 S/N prefix, ~1960s vintage

B-S_KneeLock1
View of knee clamp stud (#469) protruding through knee gib.
It appears that the stud has been grabbed with Vice-Grips.

B-S_KneeLock2
Stud has been unscrewed from knee clamp shaft (#443) by use of jam nuts.
Keyway appears to take 1/8 x 5/8 woodruff key.
Note keyway in gib barely visible behind stud.

B-S_KneeLock3
View of knee clamp crank (#757) from below knee showing attachment to clamp shaft 
by what appears to be a #3 taper pin.

It looks like the crank will need to be removed from the shaft to properly replace the key.