There are new families of gt2 pulleys since this Nov.
18 tooth 6.35mm bore gt2 pulley n 40 teeth gt2 pulley w/ 6.35mm bore.
If you are using a Nema23 stepper motor on your 3d printer or cnc machines, a 6.35mm bore pulley is necessary for the motor shaft as drive pulley. You can use a 5mm bore or 8mm bore pulley as engaged pulley.
GT2 18 Tooth 6.35mm bore Pulley works with 36 Tooth GT2 Pulley 5mm or 8mm bore.
GT2 20 Tooth 5mm or 8mm bore Pulley does with 40 Teeth GT2 Pulley 6.35mm bore.
