These pistons kits can be used with all big bore bikes. 350cc models had a standard bore of 83.20mm, 1974 Pursang and Astro had a standard bore of 83.70mm, 1975 and later Astros had a standard bore of 84.20mm and then 1975 and later Pursang and Fronteras had a standard bore of 85mm. Some cylinders can be bored out further than others. Some early El Bandidos and El Montaderos had 85mm standard bores as well.