Help! What enlarger for these lens boards ?

In cleaning up I found a number of flat metal 3 1/4 in square lens boards. Does anybody know what enlarger they are for?
Thanks,

BartAttachment 188815

Are you sure these are for an enlarger?

I ask this question, possibly the stupidest of the day, because y'r picture shows a slot on the side of the hole. These are common in boards for taking lenses. A locating screw sticking out of the back of the shutter goes in the slot to prevent the shutter from rotating on the board.

What does the other side look like? Entirely flat, or are there any surface features?

3.25" square lens boards, 25" thick with a .25" wide by .125" deep rabbet around the rear edge, was a common size many decades ago. Among the cameras that accepted these boards were Watson Press, B&J Speed Press, Graflex 3A, R. B. Speed (all 2.25x3.250, Speed Press, Auto Graflex, R.B. Series D Graflex (All 3.25x4.25, Folmer Press 3.25x5.5, Folmer Press (old style 4x5), and Auto Graflex 4x5.

I agree with Dan.
Looks to me like a lens board for a 3 1/4 x 4 1/4 Anniversary Speed Graphic... probably fits others, too.
YMMV

Edit: Jim posted a more comprehensive list

No, these boards are dead flat, metal, not wood, no rebate, about 1/8" thick. They are not Graflex type B boards. Here is a picture of what else was in the box that the boards fit. Looks like the lens stage and an extension for a Bessler 67, except those boards were 2 5/8 sq.Attachment 188843

I have some of these somewhere, and I think they came in a box for a Polaroid MP-3 with a Copal and Pronto shutter for that copy camera, but I don't have it out to measure them...

That's my bet...

Steve K

Steve-
Thank you very much. I think you are right. I had several MP-3 outfits that I bought for the lenses, shutters and bases and dismantled. I'll bet I saved these from that project thinking I could make a "top hat" lens board for the 7x17 outfit I just sold off.
Bart