Parametric Z bracket

I needed a rear Z-bracket to take some of the weight of my Netgear 48-port switch off the rack ears at the front of my Ikea Lack rack.

This has nice rounded edges and a countersunk screw hole for a 8mm diameter wood screw (thread is about 3.5mm, head is 8mm).

I guess the thickness (```wall``` variable) could have been a bit thicker, but the ABS print works fine.