Hi rob
the safety catch supplied by trapworks .co.uk sound very much like the safety catch I designed several years ago. At the time, I was trapping rats.
using 110 and 116 bodygrip traps I found the safety on them was too cumbersome and caught up on the traps and caused mis-fires.So I designed a small safety catch made from thin (1mm) stainless wire. this comprises of a piece of wire 4" long it is folded into a U shape. in the middle of the U
you form a 1/2" circle in the wire. On the two ends of the wire you form 2 1/4 "circles. These are the opposite way round to the one in the middle.