How do I cleanly cut threaded stainless .24" rods?
A 4.5 inch angle grinder with a thin cutoff disk is the tool I'd reach for first, after threading the nut on. 

If you don't have one but do have a circular saw, and the lengths you are cutting allow, an abrasive cutoff blade in the circular saw can also work. This one is listed for less than $2.50



Expect sparks. Clean out all sawdust if you use one of these in a saw that you also use to cut wood with.

For larger scale projects they do make a 14" chop saw version.

You can additionally clean up the cut threads with a triangular file or a thread-restoring file.