how is the keel fixed on the angle steel? There is no hole in the angle steel and it is so thick. How can a hand drill drive a self-tapping screw into it? I think this is what the questioner wants to know.

The first few people said to drill self-tapping screws with hand drills, which everyone knows, and you have to tell them.

I am like this: since the angle steel is so thick and has no holes, if you use a 5mm self-tapping screw, you should first use it to drill a hole with the keel, then use the self-tapping screw to lock it, then use the drilling hole at the other end, then use the self-tapping screw to lock it, then drill a hole corresponding to the middle section of the keel, and finally use the self-tapping screw to lock it.