15 HOLES BUR BLOCKS – Aluminum, Autoclavable – 10 FG Holes, designed for any instruments with FG Shanks (Friction Grip: 19mm) and FGOS (FG Surgical: 25mm) for High Speed Headpieces; and 5 RA Holes, designed for any instruments with RA Shanks (Right-Angle Latch: 22mm) and RAOS (RA Surgical: 27mm) for Low Speed Headpieces.