Micro 100 QT-250-C4 Boring & Grooving Bar Holders; Inside Diameter (Inch): 1/4 ; Inside Diameter (Decimal Inch): 0.2500 ; Outside Diameter (Decimal Inch - 4 Decimals): 1.5748 ; Overall Length (Decimal Inch): 3.0723 ; Head Diameter (Decimal Inch): 0.8