THE SIZE IS THE HOLE (I.D)
2mm = 2.4mm
3mm = 3.3mm
4mm = 4.3mm
5mm = 5.3mm
6mm = 6.3mm
8mm = 8.3mm
10mm = 10.10mm
2mm 3mm 4mm CAN USE WIRE UP TO 1 SQ mm (2mm)
5mm 6mm 8mm 10mm CAN BE USED WITH WIRE UP TO 2.5 SQ mm (3.8mm)