This steel 4-bolt center main cap is the best way to counteract the flexing of the Mini's 3-main bearing crankshaft, and is considered a must for race application. Fits all 1300, A+ or Austin America blocks. Thrust surfaces are cut-in, but must be finish-ground to size. Line-boring of the block will be required to install. The two extra (outer) holes accept 3/8" bolts.