Guides for a beverage crate roller board

I made a rolling board for our drinks crates. I needed some sort of guides to hold the crates to the board. this is what you can find here. 

The crates we use are for 12 bottles of 0.75l. These are common here in Germany.

I made a corner guide and a centre guide. The rolling board holds two crates. So I needed 4 corner pieces and 2 middle pieces. You need to mirror the corner piece for the right guides.

I used a screen printing plate for the board and 4 rollers underneath.