The line between the points is then lifted off the surface slightly, and allowed to snap back. 115mm body with accurately machined point, knurled locking screw and corrosion-resistant finish. The opposite end of the line is pulled tight, and the string pressed against the surface to be marked. A small nail tacked in position also works well if you’re working alone and the clip seems unwilling to stay put. The chalk-covered line is then stretched between points on a plane, often using the hook at one end to hold the string in place. A line coated with chalk dust is stretched PLUMB LINE PLUMB BOB POST 6'.
When the line is pulled from the chalk box, chalk adheres to the fibers of the string a gasket at the mouth of the chalk box insures the coating is consistent. Suspended from a line, the plumb bob hangs absolutely vertical when it stops. The metal or plastic case has a crank for retracting the line and contains a reservoir of powdered chalk (usually red, blue, white, or yellow in color) that can be purchased in plastic containers for refilling. Cotton string is generally preferred because its natural fibers retain the chalk well, don’t stretch, and leave a neat line. The chalk box consists of a string with a hook on its end and a convenient case into which the line is reeled when not in use. Lines of more than twenty feet become less and less accurate as the distance increases. Its chief advantages, then and now, are that it can mark lines on rough surfaces (where pencils or other markers would be difficult to use) and it will make long, straight lines beyond the reach of any standard straightedge.
It’s also known as a chalk line and snap line. It is used to mark straight lines on a surface and, like so many tools that seem positively elegant in their simplicity, the chalk box as we know it today has been around for many, many generations. I’ve admired this deceptively simple tool since I first saw my father use it decades ago.
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