Help identifying this accessory?

[siguii]

Can anyone tell me what this is? My first thought was some kind of slide duplicator, because the square end holds a 35mm slide, but it's just a hollow tube without any optics. It's also not apparently adjustable but is very heavily built. The other end has Argus C3 threads. I don't know whether it was meant to attach to an Argus or if that's just a coincidence, but it was in a box that also contained a couple C3s and accessories so it seems to be the most likely case.

 

[Ghostman]

Could it be part of an old slide viewer?

 

[snapguy]

slides?

Looks to me like it might be a slide copier. Perhaps a piece of frosted glass is missing? Does it screw into the front of the C3 lens or into the lens mount? Gotta have some optics somewhere. Looks like I might be homemade.

 

[siguii]

It screws into the lens mount, which is what confused me.

 

[AgX]

A camera focal plain shutter could also be used to control (contact copy) exposure of something within that holder. But then a feature to hold a second material is missing at that thing.