This is a 8mm Z Rod Cap / Bracket & L Bracket for use with Aluminum C Channel for a Printrbot.
This allows you to not just support in and out movement of your z rods but also back and forth movement as well.
I have my printrbot set up with 2 extruders, and have it in an enclosure. I am using a modified sand blasting benchtop cabinet for the enclosure and want to secure my printer inside the enclosure as well as stop any unnecessary movement. I plan to connect these to the inside walls of my enclosure, but I m sure angled brackets could be designed to secure to a base, or table or additional part coming off of the Printrbot base to create an "A" frame type design similar to a lot of the Reprap designs.
I designed this to fit inside aluminum c channel that is easily found at Homedepot. I dont remember the size but the inside channel where these parts would fit into is 3/4 inches or 19mm.