5" HAND WHEEL 4 SPOKE DISHED CAST IRON 1/2" SQ HOLE INDUSTRIAL MACHINE valve ect
The wheel center boss is 1/1/2" dia x 5/8 Thick with a 1/2 Square clearance hole [ NOTE 1/2" IS BIGGER THAN 12 MM ] A quick guide this hole will fit a 1/2" socket wrench square spot on. MY LOC (TALL BOY).