It's called a pump rotor. Approximately 4" diameter, solid steel. Weight: about 160 lbsThe reason's pretty simple: you can zercher squat just about any object that will fit in the crooks of your elbows. Sandbags, rocks, barbells, odd stuff, or heavy pipe can be Zerchered. Plus, you don't need to lift nearly as heavy an object with the Zercher to get a challenge since the object being lifted is in front of the back rather than directly over it.
The practicality of the Zercher squat doesn't end there. The human body is capable of lifting stupid amounts of weight with the back squat but how much heavy shit do you really pick up land put down like that in real life? Most often, the said pain-in-the-ass heavy object that needs moving is going to be in front of the body, not above it, nicely put in position with the help of some sort of rack. Life's rarely that convenient. No, you're going to grab it in a manner that looks sort of like (although not exactly the same) as a Zercher Squat.
The Zercher's also a lot more of a full-body exercise than many of the other squat variations too. The arms and the upper back muscles really get pulled into the torture session. The abs are also pulling some major overtime here too since they've got to stabilize the spine. I also find this squat variation a lot easier to go ass-to-grass (ATG) on this one, if you're into that.
By the time I got around to taking this picture, I wasn't that into ATG!
What I think that I love most about the Zercher Squat is that it works so well in conjunction with farmer's walking. As soon as I finish up my squatting, I just start walking with the weight (usually the sandbag) in my arms, cradling my little bundle of miserable joy! It's a brutal combination!
It makes sense that the Zercher is so awesomely convenient. Ed Zercher's workout area, according to straighttothebar.com looked as much like a scrapyard as it did a gym. Zercher regularly trained with oddball pieces of steel that he picked up here and there. Clearly, he was one of a few strongmen who relied very heavily on improvising. With strongman and the whole "old is new" mentality out there amongst strength trainers, The Zercher Squat offers a perfect blend of practicality and performance. Give it a try and you won't be disappointed.
Good description of Zercher execution