Plain Plug Gauge for Nail Counterbore ID Go Size 10.500 to 10.501 Cy. 0.001 Len. 20 to 21 or Std with Mark for 8.000 / 8.101 NOGO 10.519 to 10.520 Cyl. 0.001  Gauging are should have lapped finigh. Gauge No. PPG 10500.10520 