Ibedayank
From Sheldon Brown:
A single-speed (BMX) freewheel is a modular unit, consisting of a single sprocket and its associated freewheel (coasting) mechanism. These have standard 1.37" x 24 tpi threads, and fit on any hub that takes a thread-on freewheel. This includes BMX hubs, track hubs, and multi-speed freewheel hubs.
I think the OCC chopper will accept multi speed freewheel.