You should be able to get away with ball berings (not needle) for any HPI clutch bell heavy duty or not I've used them in Clutch bells all the way down to 11 tooth on my MT2. Note on non heavy duty and especially smaller tooth CB you will need to stack multiple berings to make up the gap or use washers. It took 3 and a small brass washer in a 12 tooth non-heavy duty for example.