My first thingy upload.
It is a derivative of Brooke's printrbot Y-bar end to include a tab to hold a screw which will hit the Y axis limit switch.
Can be 3d-printed.
This part comes in two variations. I have an early printrbot and the part is taller than the one in Brooke's CAD files. I presume the new printers use the short version.
The long version ends in 25 because it is about 25mm tall.
(mouse over to see the full file names)
It is similar to a thing by buckyball but has the hole in a different place.
The hole is where I think it needs to be for my printrbot - this may vary from bot to bot.
I think you will find buckyball's http://www.thingiverse.com/thing:22343 is the current one to use for printers with the lower base.