A removable bracket must be attached to the frame of a machine tool as a support. The need for interchangeability dictated bolting. Clearences and accessibility to the bolts required a pattern shown on the image. SAE Grade Number 7 bolts are used, bearing strength of plate = 60000psi and the thickness of the plate is 3/8 of an inch. For a factor of safety of 3, what diameter standard bolt should be used?