LOCKING SYSTEM: Special Design to Lock Both the ROUND and the SQUARE Tap Shank in Slots for Maximum Gripping (No Slipping), TAP SHANKS: ASME B94.9-1999, MAXIMUM PRECISION: Precision Made for Tool Shanks with H6 or Better Tolerance, EXTREME PERFORMANCE: Designed to provide Maximum Ridgidity and Better Tapping Performance on your Taps , SPECIAL DESIGN: Note that these collets do not ” COLLAPSE” to the same degree as standard ER Collets. Our SLOTTED Design is for maximum clamping on the entire Tap.