Inspired or reminded by gnu's Cable Clip (Parametric) thingiverse.com/thing:39901 I remembered having made this openSCAD file that will generate three types of pipe or cable clip with either sharp or smoothed edges. I never finished making it into a proper library though as all the code needed re factoring. Here it is though, you can make the nail down sort of cable clip a split screw down type and an holder for a zip tie.

Edits
v0.95 - Slight tidy up for use with the customiser