The stl files are configured for 23.8mm ticknes, if your shelf is a little below than 23.8mm you can use it as this.
But i think is better to adjust the parameters with the .f3d file a little more 0.3mm at your value and use the two bolts for final tightening.
But don't forget this is PLA bolts and not Steel ... don't tight to much ;) ....
I use two 3.5x40 screws to assemble 
Place the bag inside the two arm et clip it.

I join the parametric f3d file if you want to use with your own values ...