Parametric Z base printed clamp/spacer

Prusa's rod clamps are all well and fine, but I don't actually want to adjust the spacing from Z smooth rod to frame.

Here's a one-piece connector with optional bearing holder.

Fully parametric, including rod spacing. Match with blddk's derivative of my Integrated Z motor mount+frame vertex+rod clamp - http://www.thingiverse.com/thing:12215

Overall size of the part comes mostly from washer_diameter and the spacing distances.

horiz_distance is the distance between the center of the sm