Tim+ pretended :
As far as I can make out it consists of a wiring kit and the
> addition of a second threaded towing eye socket. The car I'm
> looking at has two bumper holes for a towing eye but only one of
> them has the threaded insert.
The towing eye is a standard thread, bolts to suit are easy to source or you could pick up a towing eye from a car scrap yard.