Plain Plug Gauge for Sleeve ID Go 6.5 to 6.501 Cyl. 0.001 Len. 80 to 81; with tapping of M4; NOGO 6.521  to 6.522 Cyl. 0.001 Len. 10 to 11 / Std. Gauging area should have lapped finish. Gauge No. PPG 6500.6522