Probably a little bigger than needed but I don't think you'll have to worry about breaking them…  These can be used with straps up to 35mm wide, .STEP file included in-case you would like to modify. All edges in contact with the work piece have chamfers to prevent any elephants foot or imperfections on the edge pushing the work piece out of square.

I printed with 4 x 0.6mm walls and 35% cubic infill but you could get away with less if you would rather save on filament.  

I've printed in PETG but PLA would also be fine.