Judging from the pallette, I'd say they're 1/2" rope/6" Sheaves. The extra size on the anchor point is because a double sheave will have double the weight on the attachment point over what a single sheave block would have. Your individual line pulls are added on that attachment point, so you need more anchor capacity, that's why those are larger shackles. With 3 single blocks and one of these, I could rig just about anything.