I designed this holder to keep the cylinders off the shelf and save some space as I'm cleaning up and reorganizing my shop. The holes are tilted at 4 degrees so they should not work themselves out although they would probably be fine if horizontal. With that in might though, make sure you don't mount the holder too far from the front edge of the shelf though. The wall behind keeps them from going all the way through.

I printed it in PETG with 2 walls and 25% cubic infill and it's very rigid. It's held up with 6 #10 x 7/8 pan head sheet metal screws. I added modifiers at the holes to solidify them for the screws. I also added helper discs because my first one peeled off the plate mid print.