Drive chain

To choose the drive chain of your motocross or enduro motorcycle you can guide yourself by this small table for guidance.

420 chain -> Ideal for 50-65cc motorcycles. Do not use on motorcycles over 150cc.
428 chain -> Ideal for 85-125cc motorcycles. Do not use on motorcycles over 150cc.
520 chain -> Ideal for motorcycles from 200cc to 500cc.
525 chain -> Ideal for off-road motorcycles over 500cc.
Chain with seals (428, 520, 525 O-ring) -> Ideal for enduro. It is heavier but you don't have to grease it as often. For motocross they are also used at an amateur level to avoid so much maintenance and wear.
Number of links -> It depends on the motorcycle model and the tooth ratio you have. It is best to count the links you have in the current chain and if you do not modify the teeth of the crown and the pinion much, it will be the same length.
When in doubt choose a chain with more links and then you can cut it to size.
Sprockets -> You will find the correct ones by first selecting your motorcycle from the menu.