... very high penetration rate .To secure the bit from diameter loss, the gage protection inserts have got shorter length and greater angle ... bearing seal.Main Type Available Size: 6",6 1/2",7 1/2",8 1/2",9 1/2",9 5/8",9 7/8",12 1/4",17 1/2", etc ... location limit, compared to conventional rigs where sound averages up to 120 decibels. Main Type Available Size: 8 1/2",9 1/2",9 5/8 ...