Don't drop the plugs down the hole. The chance of bending the electrode on the end is pretty good....then they won't be gapped right, and may not work at all.
Of the 2 "common" spark plug sockets, it is the smaller one.....sorry, I can't remember the size. If you can't find one with the rubber insert, just put a small piece of paper between one edge of the socket and spark plug and it should hold the plug in the socket so you can gently put it in the hole and get it threaded in.
And you will also need a 6 inch extension to reach the bottom of the hole.
For the compression tester thread size, just use a spark plug to match up the thread.