Stainless steel, passivate per woodward governor specification no. Sp-151, 33 to 37 hardness rating, rockwell c scale, 0.550 in. Min, 0.555 in. Max od, 0.435 in. Min, 0.436 in. Max id, 0.052 in. Min, 0.057 in. Max diameter 180 degrees apart on 0.460 in. Bolt circle dia, 1/4-28 unf-3b thd