If you want to fit one , have a read at "the idiots guide" at the top of the papge. There is an idex as well.
The correct spring if you want to fit the safety is the same as the one for the Hawk mk3 https://www.gunspares.co.uk/products/24527/Hawk-MK3/ part no CS130. However the safety was never great and you are better leaving it off and using
https://www.gunspares.co.uk/products/24554/Victor/ CS 131 from the Victor, which is tensioned by the straight leg going under the trigger pin.