I like these indicators but they are way too sensitive. They indicate when a competitor hits the post instead of the steel target. Also, if you have a multiple array of targets hanging off a common shaft, hitting one target sets off the others on that array.
As to physically mounting them on the steel itself I drilled two holes in the target and mounted a peice of conduit about 12” and mounted the indicator on that. Conduit sticks out 7” at 2 oclock.