"I was fixing upvc windows to steel roof supports and thought I would have to drill and tap the holes I did not believe they would work but they did it is worth using a depth gauge as once the thread bites they realy travel"
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Review 4 for Self Drilling Screws 5.5 x 55mm Pack of 100
"took a while to get the hang of using these. had to pilot the holes as these do not drill their way through steel on their own. seemed to work best with a pilot hole, a very very slow drill speed and getting a shoulder behind the drill it for a lot of shove. Once this method was sorted, they were actually pretty useful."