Plain Plug Gauge for ID of Angled End of Body (Go 12.003 to 12.005 Cyl. 0.001 Len. 50 to 51 & NOGO 12.095 to 12.1 Cyl. 0.003 Len. 10 to 11 ro std. Gauging area should have lapped finish. Gauge No. PPG 12000.12100