Micro 100 QDH-4125 Boring & Grooving Bar Holders; Inside Diameter (Inch): 1/4 ; Inside Diameter (Decimal Inch): 0.2500 ; Outside Diameter (Decimal Inch - 4 Decimals): 0.4372 ; Overall Length (Decimal Inch): 2.3130 ; Head Diameter (Decimal Inch): 0.75