Plain Plug Gauge for Locking Bold ID (Go Size 10.5 to 10.504 Cyl. 0.002 Len. 50 to 51 & NOGO 10.567 to 10.570 Cyl. 0.002 Len. 10 to 11 or Std. Gauging area should have lapped finish. Gauge No. PPG 10500.10570