8" 1/4"-20 Screwback Master Support Lap

The Precision ground flat and parallel Screwback Master laps ,Its used as a base plate for other laps. 1/4" thick and are not charged with abrasive. The Lap is ground flat and parallel and is used as a base plate for other laps. The ground flat and parallel Lap.It is used as a base plate for other laps. Master Lap is 1/4" thick and are not charged with abrasive in 1/4"-20 right thread.