Z-extension for Maker Select v2

Chopped off the lower part of a [recent Z rear brace with extension part](https://www.thingiverse.com/thing:2990990) I did, in case someone wants the Z extension without the Z rear brace.

This puts no stress on the upper cross-brace of the frame.

**TIPS**

- I printed these with large flat side on the bed (the side with the hex nut holes). It puts a lot of supports in the 2mm gap -- you can remove these with thin needlenose pliers, but biggest help was to use the scraper that came with t