The Click Rule, from chapter 1 of the manual for blind woodworkers.
The Click Rule is a metal tubular device seven and nine-sixteenths-inches long that houses a threaded steel rod that clicks at every one-sixteenth inch as it is moved to new settings.
The threaded rod has raised threads every half-inch. The metal tube has two flat rectangular stops or fences mounted on it. One stop or fence is located precisely at the open end of the tube and the raised thread rod protrudes through it. The other stop or fence is positioned exactly six inches along the tube from the stop at the open end of the tube. The front fence at the end of the tube is exactly one-quarter inch thick and it is five-eighths inch wide by one and three-eighths inches long. This fence lays on its long edge. The back fence is seventeen-sixty-fourths inch thick by three-quarters inch wide by fifteen-sixteenths of an inch long. This fence is fitted around most of the tube and stands vertically on its width.
A seven-inch piece of the threaded rod is inserted into the tube and a knurled locking knob is screwed into the top of the threaded rod through a long slot that has been machined into the tube. The threaded rod can be extended from or retracted into the tube by sliding the knurled knob with the rod attached. A small BB with a spring has been milled into the stop at the very end of the tube so that as the BB rides over the threads, a clicking sound is heard and felt. Each click corresponds to one-sixteenth inch. The Click Rule is accurate to one-sixteenth inch.
The Click Rule comes with three 12-inch extension rods that screw into the end of the Click Rule raised thread rod and into each other. The Click Rule uses a 10-32 thread patern.
The Click Rule measures from the end of the protruding threaded rod to the nearest face of the rectangular stop positioned at the end of the tube. Remember this carefully while reading the following descriptions of how to use the Click Rule.
Helpful Tip: In practice, instead of having to count clicks for every sixteenth of an inch, the raised threads at half-inch intervals can be counted to position the fence close to a measurement, and then the final clicks can be counted to fine-tune the exact measurement. Therefore, the user can count the number of raised half-inch marks on the threaded rod protruding from the end of the tube and count the extra clicks in sixteenths of an inch to determine the measurement.
Remember that with the Click Rule, the raised thread must be positioned just outside of the fence so that it can be felt with your fingernail.
How to measure with a Click Rule It’s time now for a test measurement. To use the Click Rule to measure exactly two inches, loosen the knurled knob and push the knob to move the threaded rod out of the tube. Push the rod out until four of the raised half-inch threads can be felt. The fourth raised half-inch mark will be just a fingernail away from the stop or fence. Now you are exactly at the two-inch mark so tighten the knurled knob to lock the rod in place.
For the Click Rule you must be able to feel the raised thread outside of the fence. In this test measurement it is the fourth raised thread outside of the fence that measures exactly two inches.
Now let’s do a more difficult measurement. To use the Click Rule to measure four and three-sixteenths inches for example, loosen the knurled knob and push the knob to move the threaded rod out of the tube. Push the rod out until eight of the raised half-inch threads can be felt and the eighth mark is just a fingernail away from the stop or fence. Now you are exactly at the four-inch mark.
Next, slide the threaded rod an additional 3 clicks to set it for the additional three-sixteenths inch. Now tighten the knurled knob to lock the rod in place.
If the distance to be measured is between six and twelve inches, then simply measure from the end of the rod to the inside face of the second metal stop and add six inches to your measurement. This precisely placed second stop in the Click Rule eliminates the need for a six-inch extension piece.
Outside measurements with the Click Rule. Outside measurements can be determined easily with the Click Rule. To measure the length of a board, it is helpful to butt the end of the board against a fence or other stationary piece. Slide out the threaded rod as necessary until the end of the threaded rod butts against the stationary piece and the inside of the stop or fence at the end of the tube fits snugly over and against the opposite end of the board. Probably you will have to set the Click Rule to a rough measurement and then carefully position the tool against the stationary piece and adjust the measurement until you get it exactly.
Once again, if the measurement will be between six and twelve inches then measure to the inside face of the second fence. Remember to add six inches to the noted or “clicked” measurement.
To measure the outside measurements of a box it is helpful to clamp a block or piece of wood to one outside face of the box. Slide out the threaded rod as necessary until the end of the threaded rod butts against the block and the inside of the Click Rule stop or fence fits snugly over and against the opposite outside face of the box.
Approximating measurements to one-thirty-second of an inch. Remember that the Click Rule measures only to the nearest one-sixteenth inch. If the Click Rule fence fits only loosely against the opposite outside face of a box or the end of a board, then the actual length of the board probably is roughly one-thirty-second inch less than the measurement shown on the Click Rule.
Inside Measurements with the Click Rule. With some practice, accurate inside measurements can be taken. Remember, the length of the Click Rule is seven and nine-sixteenths inches. To make an inside measurement of a small box or drawer or door opening inside a face frame, for instance, position the Click Rule so that the threaded rod fits against the inside face of the box and the backside of the Click Rule fence fits snugly against the opposite inside face of the box. To account for the thickness of the first fence, be sure to add one-quarter inch to the Click Rule measurement noted. But if the measurement is between six and twelve inches so that you are measuring to the backside of the second fence, then you will have to add an extra seventeen-sixty-fourths inch to the measurement, that is, an extra one-sixty-fourth more than the extra quarter inch to account for the slightly thicker size of the second fence.
Extending the length of the Click Rule. You can extend the length of the Click Rule by adding threaded rods that screw into the Click Rule. The extension rods will accommodate longer measurements.
Again remember that the Click Rule measures only to the nearest one-sixteenth inch. If the Click Rule fence fits only loosely against the opposite inside face, then the actual measurement probably is roughly one-thirty-second inch greater than the noted or “clicked” measurement.
Measuring inside a cabinet with face frame: A cabinet opening with a face frame or other obstruction makes it difficult to use the Click Rule.
It may be easier to take two straight narrow boards that fit easily within the cabinet opening. Overlap the boards and position the end of one board against the left side of the cabinet and position the end of the other board against the right side of the cabinet. Pinch the boards against each other and either clamp or tape the boards to maintain the position and measurement. Now use the Rotomatic or Click Rule to measure the length of the boards. That length will equal the distance between the cabinet sides.