Parameterized cable gland

This is a remix based on the NUT JOB factory https://www.thingiverse.com/thing:193647

The gland size is control by these three variables.

gland_inner_diameter = 10; // The diameter of the inner channel. the outer size is always +5mm of the inner.
gland_rod_length = 35; // The length of the rod
gland_nut_height = 12; // The length of the nut