What is a line block?
A line block is a small, roughly "L" shaped block with specially made grooves to which you can secure a brick line.
Line blocks are frequently used by bricklayers (in conjunction with a brick line) as an aid to keeping brick walls horizontally level as they are constructed.
Two line blocks are used to suspend a brick line between two points on a brick wall. The resulting guideline allows you lay level bricks confidently and circumvents the need to check with your spirit level with each brick you lay.
Line blocks can also be used to take a brick line around a 90 degree angle.