There are a couple of different types of line block available on the market, though their chief function remains the same: to provide anchor points for a brick line to be suspended between and used as a guide to laying bricks straight and level.
Some traditional line blocks are made from hardwood though the majority of modern line blocks are made from plastic.
“Mason’s mate” line blocks are slightly different from typical line blocks insomuch they have a lipped 90-degree angle which can be attached to the top corner of a brick. A brick line is anchored to its line hooks.
The advantage of a mason’s mate line block is that you can secure it to the corner of a brick and pull the line taut without someone having to hold it in place. The disadvantage is that it is designed to attach only to the top course of bricks.