The rack mount can accept up to 4 pi's or similar boards. Its printed in 2 halves and can be printed on an Ender 3 at 45 degrees. There's 3 main bodies, one with just 2 pi slots, one with 2 pi's and 2 keystones, and one with just 12 keystones you can mix and match halves. The pi is meant to be mounted using 6mm standoffs, but I've included printable standoffs if you don't have any and you can just use a m2.5 or m3 screw and nut to hold it in place. The 2 halves are held together with 3 M3 screws and nuts, the rest of the parts are just threaded into plastic. M3x10 is the max length of screw i recommend for this project with the exception of the pi if you need a longer screw there that should be fine.