Older BMX type hubs will be identical in the thread department
Newer BMX hubs use an over size body and new type of freewheel which is smaller, the hub necks down to carry it, IIRC it's more similar to a cassette system but I will have to check, the sprocket body is tubular in shape and much wider.
You could once upon a time in the 80's get standard pattern screw on freewheels that were smaller than 16 tooth with re-engineered pawls and teeth inside them to make them smaller but your chances of finding one are slim.