Unistrut Channel Trolley Track - 4.75 Feet Galvanized Steel U Channel (1-5/8" Wide) for Heavy-Duty Storage & Garage Organization - 12 Gauge Metal Track with Groove Back - Perfect for Shelving, Pipe Supports & Workshop Systems (Silver, 1 Pack)

I'm using jacks to shore up three joists on 2' centers, with paired channel struts across, both on the ground and bearing against the joists. Four-foot channels would be a little too short, so I was pleased by the length of these. I would have preferred solid back rather than perforated, but perforated wasn't a problem.No way to pour a proper footing in the crawl space, but the ground is dry and hard, good enough, I hope. I wanted to put down a poly underlayer to reduce the possibility of rust in case of moisture, and found that I needed to file off the sharp edges at the ends, where they were cut to size with a saw. Not a big deal.Good product. I got what I expected. No surprises.