Micro 100 QSG-312-500 Boring & Grooving Bar Holders; Inside Diameter (Inch): 5/16 ; Inside Diameter (Decimal Inch): 0.3125 ; Overall Length (Decimal Inch): 4.8000 ; Head Diameter (Decimal Inch): 0.8750 ; Series: QSG ; Manufacturer's Part Number: QSG-