Odd ID on MF Slide Mount

[jd callow]

I have a bunch of medium format wess antinewton glass slide mounts. THe outer diameter is the standard 8.5cm of a medium format mounts. The inner diameter is 3.2 cm by 6.8cm.

It appears somewhat large on the short side for a 35mm panoramic. Any ideas?

 

[Fintan]

could be the same size as the panoramic mask for hasselblad 6x6 film backs