One of the fascinating things about our profession is that, along with laser levels, cameras that scan inside sewer lines, and other 21st century marvels, we work with simple tools that have been around for centuries. The humble string guideline, used by ancient Egyptian, Greek, and Roman builders, is an example. Carpenters routinely use one to straighten walls, and masons follow a string line for just about every course of bricks or blocks they lay.
Before they can follow a string line, however, these craftsmen must set it up. This typically entails anchoring one end of the string, stretching it tight, then anchoring the other end. In addition, they must set it in exactly the right position, and they need to do it quickly.
Carpenters use nails or screws as anchors, learning how to drive them in the right spot and angle. Masons don’t have it so easy. In addition to the difficulty of driving a fastener into masonry, there’s the problem of marring and chipping the surface. To avoid these problems, masons usually use line blocks. These hook either on the outside of a “corner lead” they’ve built using a level or on a square story pole they’ve set up. The line blocks at each end are held in place by tension created when the masons pull the line tight.
While line blocks are precise and easy to use, they don’t work for pulling a line from an inside corner, where there’s nothing to hook them to. I’ve acquired numerous line-holding accessories and come up with a variety of makeshift solutions. One of the best has been to attach a line to a block of wood and clamp the block in place. It worked but was clumsy and took too much time.
The Bon Tool Jag Clamp employs the same principle, but it works a lot better. It clamps to the face shell of cored blocks or the width of a brick. The clamping mechanism is a strong spring clamp, so it sets up quickly. Attaching a string line to the clamp is easy; you simply wrap a couple of turns around a tapered rivet that serves as a cleat. When set, the string lines up precisely with the edge of the brick or block. This is a special-purpose tool, but one that one that masons working from inside corners will use repeatedly as they work up a wall. They won’t use it every day, but when they do, it will be handy.
Bon Tools makes two Jag Clamps: the 21-290 and the 21-291. The 21-290 is limited to clamping to surfaces that are 1 1/2 to 2 inches in width, which is great for most CMUs (concrete blocks) but doesn’t work for bricks. The 21-291 is adjustable and can clamp over surfaces 5/8 inch to 5 1/2 inches wide, including the face shell of standard CMUs or the width of bricks.
A pair of 21-290 Jag Clamps costs $26. A pair of the 21-291 adjustable Jag Clamps costs $39. I’ve found that the extra money for the more versatile 21-291 is well-spent. Although it’s primarily a masonry tool, carpenters might put it to use for tasks like straightening floor joists or rafters. bontool.com
