Micro 100 QTHM-520 Boring & Grooving Bar Holders; Inside Diameter (Inch): 5/16 ; Inside Diameter (Decimal Inch): 0.3125 ; Outside Diameter (Decimal Inch - 4 Decimals): 20.0000 ; Overall Length (Decimal Inch): 2.8000 ; Head Diameter (Decimal Inch): 0.