Compare 1.375x24 TPI and M30 freewheel sizes on a BMX style flip-flop hub - YouTube
Amazon.com : Hycline Single Speed Bike Freewheel, 16T Compatible with 1/2'' x 1/8'' Bicycle Freewheel Threaded Type Freehub Replacement Parts (Black) : Sports & Outdoors
Freewheels - BMXGuru.com / C&W Cycle
ORIGINAL Ruby FREEWHEEL SINGLE All Sizes & Colors Available, BMX BIKE | eBay