It mite be for the same thing as the 4 1"sq. holes in the M105 beds
OT!
A friend of mine was an electrician on an aircraft carrier. The commander of the carrier was on a tour of the ship one day and saw a hole in some big control panel. (modular panel) He told them to "plug that hole", and that he "didn't care what they put in it."
So they built a little panel with two lights and a switch. If the switch was in the middle, the lights were off. If the switch was one way, they flashed together, and if it was the other way they
oscillated. They gave it a part number, and wrote a couple of pages of procedure to go with it.
If you were doing (whatever, insert something here) you put the switch to the left. If you were doing (whatever, insert something else here) you put the switch to the right. Otherwise you left it in the middle.
When he was telling me about it he said he always wondered how many
sailors moved to another carrier and looked for that panel. He also wondered how many of them got yelled at because the people at the new ship didn't have a clue what the
sailor was talking about and figured he didn't either.
Maybe the bracket on the M107 and the holes in the M105 are something like that?