OK, So if you look at the title and say ??@?#?$%%$@, it's time for a little umbrella-holder intro.
Umbrella holder AKA umbrella swivel is a piece of equipment that is meant to attach a small strobe to a light stand. They come in verity of prices and flavors, but one thing is common to all. They have a hole on the bottom to connect to the light stand on one end and a metal stud / hot shoe / cold shoe that attaches to a small flash on the other end.
Wait - didn't you say they are called umbrella holders? Well, yes - this is because they also have a dedicated shaft to insert an umbrella, either reflective or shoot through.