Mason line is a product used to make straight lines and a leveled surface. It is useful when laying patios, posts, footings, and more. The product is necessary during such jobs as you will no longer need to pick up the level numerous times. Another excellent part about this twine is that it won’t sag like other twines.  Available in 500’ and 1000’ rolls and a variety of hi-vis colors.

https://www.ustape.com/product-category/brand/stringliner/