This is a parametric part I designed for my Printrbot+ (wooden extruder). It replaces the little wooden latch, guides 3 mm filament, and holds the nylock nuts so you don't have to.
My first thing!
The holes and hexes are designed at 108% of the ideal size. My printer likes to make tight holes, in spite of pretty good calibration every which other way, and this gave me a good fit. Your mileage may vary.