Many chains have the chain size stamped directly on the chain links.
Chain sizes #'s 35, 40, 41 & 420 are used in the Fun Kart and Mini Bike Industry.
An 11 or 12 tooth clutch sprocket usually indicates the use of # 35 chain.
A 10 tooth clutch sprockets usually indicates the use of #'s 40, 41 or 420 chain.
Make sure you order enough chain, any extra links can always be removed.