A rethreader handle is very similar to that of a screwdriver. It has ridges for improved grip and a collar to prevent your hand from slipping down the tool.
Rethreader shank
The working part of the tool consists of a shank, the end section of which is threaded. The threaded section has flutes (unthreaded channels) to collect and remove any waste material.
Where the flutes and threaded sections meet, a sharp edge is created, which can push damaged threads back into place and also shave off small damaged sections.