This is really more for beginning ship modelers. Experienced ship modelers, and probably most beginners too already understand the way a standard rigging block works. It’s basically just a wooden block with a pulley, or sheave, inside a slot. There are different sizes and types, and there are single, double, and triple blocks, and just about ever wooden ship model needs at least some number of blocks.

Standard Amati single-sheave walnut blocks
There is one mistake I occasionally see regarding blocks. To me, it’s such an obvious error that it detracts from the entire build. But, the thing is, after a modeler completes so much work on the hull, deck details, masts, and all, I really don’t want to point out the error. So, I figured it might be best to just mention it here.
The issue is that a block needs to be rigged so that the rope passing through it, runs over the surface of the pulley.

The RIGHT way.

The WRONG way!
On the standard kit block, this basically means that with the line running as shown above, the hole in the block should be at the top.
This may seem simple and obvious. But, when building a model, it’s something that can be overlooked. Particularly since the blocks are often attached to yards and such before lines are run through it. It’s an easy mistake to make, so it’s important to catch it while you’re mounting the blocks, so you can correct the error before it becomes too difficult to do.
Heck, even those who know better sometimes mount blocks incorrectly (myself included). In fact, one of the worst examples I’ve seen is the model on the box art of Panart’s HMS Victory kit. Not sure if you can see in these photos I scraped off the Internet, but I’ve seen this box art up close and I’ve never seen so many backwards mounted blocks on a model.
So, try not to let this happen to you. Plan ahead when you attach blocks to your model. But, at least if you do make the mistake, you know you’ll be in good company. Ω