Ok the original size was something weird like 1 49/64" but somewhere along the line someone figured a 1 3/4" is fine. Oh well....Dorman part number 565-036 for brass and 555-036 for steel. Clean the holes in the block well and before installing the new ones. BTW there is no lip on the inside of the block for the plug to bottom out on. Just tap them far enough so the lip is flush with the hole. The older plugs had a deeper lip also compared to the Dormans. G.