Fixing small canvases together to make larger one

tyllwyd

Hi! My DD was doing art at school, but the teacher only had small ready-stretched canvases, so she took four and placed them in a block to make a bigger area to paint.

What I need now are some kind of spring loaded clips, so that I can fix the canvases together before I put it up on the wall. Does such a thing exist, and what are they called?

Thanks for any help!