Yea, I think I noticed that there might be two sizes.
But in any event. Drills come in lettered, numbered, fractional and mm sizes. In order to tap a hole, a specific bit size is used. For 1/4-20 a #7 drill is used.
Taps come in plug (tapered), bottoming, and starter taps. Taps are held by "T-handles" or tap handles. The end of a tap is square.
You can use just a plug tap for a thru hole, but the "kit" of usually 3 makes it easier. The bottoming tap is used for a hole that does not go completely through the metal.
Lubrication is the key, especially for aluminum. Tapping fluid is usually used. In manual tapping there is a lot of turn a little bit and reverse to break off the material. Then possibly remove the tap, clean it and back to the same old grind again. Try to make sure that for the initial turn, the tap handle is straight.
Then clean out the hole. Compressed air works if you have it and try a bolt.
The tap is hard and thus brittle and they will break. 1/4-20 is relatively easy than a 6-32 tapped blind in 304 stainless and the part your tapping is worth in excess of $1000.00 USD.
Then there are drills designed to be "clearance drills" These let a bolt bass without restriction. An "F" drill would be used for this.
See:
https://en.wikipedia.org/wiki/List_of_drill_and_tap_sizes
It looks like the typical camera screw has a close cut shoulder. Don't know how long it is, but the fastening body is usually less than that because, you don't want the screw to fall out when nothing is attached. So, the "other side" not the camera side is threaded too, but when the screw is all the way into the "other side" it will become loose and it can't fall out of the hole.