cleaned up C clamp for QiDi Tech 1 X-Axis Belt Tightening Jig

This is just Tool_A from davebpix's QiDi Tech 1 X-Axis Belt Tightening Jig, cleaned up in Meshmixer. However I'm rather new to meshmixer and didn't really know how to keep the thread detail without making a huge file, so huge file it is. Printed fine for me in slic3r 1.3.0-dev