What motor do you need a flywheel for?...1/4-28 doesn't begin to tell the story of what you need.
99.9% of all .21 motors made use a 1/4-28 thread on the end of the crankshaft.[i'm sure there is some obscure eastern european .21 out there that uses something other than 1/4-28 but I haven't run into it.]
It is the I.D. of the front bearing size used in the motor that determines the flywheel and collet assembly you will need.
K&B flywheel collets fit a 1/4" shaft......most every other .21 motor uses a 7MM flywheel collet size.
Remember,whatever flywheel collet size you need,the flywheel and collet are a matched set per manufacturer,I.E.,a K&B collet will not work with a NovaRossi flywheel.
You first need to determine the flywheel collet size you need,get a matched flywheel and collet set,and then a lathe will make it any external size you want.
Your chances of finding exactly what you need as a stock item on some motor are going to be very slim to absolutely none.
