Once entered into the screw, they need to be turned carefully by means of a tap wrench or similar two handed holder. Do not use a spanner or pliers. SPECIFICATION: No 1 -. Size: 4 mm / 5/32". For screws:3 - 6.5mm / 1/8"-1/4". Drill size:2.5 mm. No 2 -. Size:5 mm / 3/16". For screws: 6.5 - 8 mm / 1/4"-5/16". Drill size:3 mm.