new for 2021 our twin keyed flywheel from GZR racing. This flywheel fit all of the rcmk S-520 twins and GZR in-lines also fits all std single cyl engine like zenoah,cy,rcmk,and clones on the flywheel it is stamped with our star logo that key fits the std single engine. The one with no logo on the key is for the in-line This is only std rotation