Anyone knows what this is for? Looks like a clamp?

[lorenzospain]

Hi I'm Lorenzo from Spain, new here, hope someone can help me out! Found this at a Spanish second hand shop. There are four wing bolts with their individual springs in between the two wooden frames, making it possible to tighten each corner of the frame separately. Any idea what its purpose is?

 

[Jake]

It's for storing wooden tennis rackets to keep them from bowing.

 

[Sideways]

My mother's (wooden) racket was always stored clamped in one of these.

 

[Katomi woodsmith]

As above posts, I knew straight away having seen my mothers one for many years.
In addition to bowing the rackets were carried to matches in these fames for protection.