A sliding T bevel, also known as a bevel gauge, is an adjustable gauge for setting and transferring angles.
These are really useful for woodworking and tile cutting. I use them for taking angles directly from a part to compare to a protractor.

Wikipedia Explanation: http://en.wikipedia.org/wiki/Sliding_T_bevel

Steel version on amazon for comparison: http://amzn.to/28MuIaL

You will need:
(1) 1" long 1/4"-20 bolt
(1) 1/4" washer
(1) 1/4"-20 butterfly nut

I printed at 30% hexagonal infill for the handle and 35% hexagonal on the blade. The blade is 1/8" thick so you may want to go up to 40-50% infill for a really durable tool.