Originally Posted by Ballistik Mods
Mate the hpi flywheel is made to fit the hpi engine ,you will need to buy an aftermarket flywheel and nut from your local hobby shop.
hpi have a range of hop up flywheels ,try there website first.
Like the above guy quoted, the hpi flywheel fits perfect on an OS engine if you use a hpi collet. I have never had an issue with mating a hpi flywheel to an OS. I have some new and used ones available if you really need one. Just need to know what hpi car it is going on and whether or not you are mating this to a pullstart or non-pullstart engine (yes, the flywheels are different sizes for ps or non-ps use). Also, need to know what OS engine your are mating this flywheel up to.