Originally Posted by dddd

First step is to allow us to identify the parts you are using.

Post a photo of the hub. Someone will recognize it, and I would guess that it is likely as not English-threaded.

Also, the identity of the existing freewheel, post a photo of the cleaned face of it, it may or may not be French threaded either.

With the Freewheel removed, the hub threading can be gauged as non-French using an English bottom bracket cup, and can be gauged as French using a standard 1mm-pitch front or rear axle. Meshing the threads in front of a lighted background like a computer screen will show if the threads mesh nicely or if the engagement rocks instead of engage because of different thread pitch.

A French-threaded freewheel will not spin freely onto an English-threaded hub, the threads will begin to interfere after a few turns.