Can anyone identify this:

http://i65.photobucket.com/albums/h222/bofphoto/fbab5289.jpg
http://i65.photobucket.com/albums/h222/bofphoto/ff6e3c5e.jpg
http://i65.photobucket.com/albums/h222/bofphoto/2fc08eb9.jpg

it's steel, 19/32" thick, 12_1/8" x 12_1/8" square and the groove
centres are 7/8" from the edge of the plate, and I found it in my loft.

Seems far too carefully made to be just a lump of steel plate.

MTIA


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bof at bof dot me dot uk