The link you posted looks like the block is for wire, not line. You are supposed to run your Land Rover's winch wire through it and then attach it to your ATV with the shackle provided so you can extricate yourself from the river you landed in by mistake after your third beer. It "doubles" the pulling power, and since this makes it take twice as long, you get to finish your fourth beer. It is strong enough to be used on a boat, but the sheave probably isn't wide enough to take a line that won't cut into your hands when you go to trim it. (Your hands are not built to handle winch cable.) The way this ATV snatch block is built, with pieces that come together under pressure, means that when it's not under pressure (when it's on the windward side of a jibsheet, for example) it will clatter to the deck, making a lot of noise between the shackle, the cheeks, and the sheave, banging and jangling there on every wave until you tack, when the one on the other side begins doing the same. There is a reason boat snatch blocks often have rubber coatings on the outside- so the off-watch can sleep. Having to attach it with a shackle, rather than a clasp, means you will have to mouse the shackle if you don't want to lose the pin. This makes moving or changing the snatchblock quite a hassle. Boat-type snatchblocks are expensive, but there are reasons for it.
