Hard to describe, easy to use. This is a quick jig to hold wooden batons 7mm away from both edges of a plywood piece. I use plywood and batons to make my boxes, and being able to quickly space it a wall thickness away helps enourmously.
I use a nailgun, which makes it harder than just clamping, since you have to flip the piece over in order to drive the nails into the flat side. Making sure the batons are exactly 7mm from the edge is tricky without clamping, and if you clamp it then you can't lay the wood flat on the table, which makes alignment trickier. This jig holds the batons in place while you're flipping the wood. (Or rather it gives you reference edges to push the wood up to).