Ok I have a few questions about building a JGRO.

On the parts list its says cnc_dtl12 www.rockler.com -- --- HOLD DOWN CHANNEL. I quickly looked at their site. What exactly am I looking for?

The on cnc_dtl01 and 02 there is some holes marked thru all, and some that aren't marked that. Does that mean that the thru all are drilled thru both sheets, and the other one just thru the top? (pages 18 and 19 in the pdf)

This is my first machine and my set into CNC. My uncle has a mill and lathe and I am hoping he will help me build this machine. Hopefully I will learn more about machining while working on this.