Is it this stuff?
http://www.unistrut.com/Browse/cat_pg.php?P=S00_Channel

it is the 3300 on that page. Nice to know that the 100Lbs and less that i
lift are well under spec even though I have it rotated 90 deg. I would be
more worried about the 5/16 lag bolts into the rafters pulling than a track
failure.

A weston brake would be nice, or a marine camlock, but with two double
blocks even the large mill vise and rotary table are easy to hang on to.