A 5/16 bolt has a head size of 1/2" socket.
A neat trick: doesn't work for all bolts but quite a few or gets you very close.
1/4 bolt : numerator x3, denominator x2= (3/8) but 7/16" is what you need.
5/16 bolt : numerator x 3, denominator x2=. 15/32- (close to )1/2 " socket
3/8 bolt : numerator x3, denominator x 2= 9/16" socket
1/2" bolt: numerator x3, denominator x2= 3/4" socket
3/4" bolt : numerator x3, denominator x2= 1 1/8" socket.
Pretty nifty but doesn't doesn't work for all.
