Thread gauges are an unusual sort of tool. When you first examine them, they may remind you of jackknives (also known as pocket knives) because of all of the separate instruments that are connected together and swing out from a central connecting bar. In many ways you could say that these are the jackknives of the fastener world. If you have never used one of these multitool tools before, here is how to use a thread gauge.
Pick up a Screw or Threaded Bolt
Whatever the fastener is, it has to have a thread winding around it or winding around the inside of it (if you are trying to measure the thread of a hex nut, for example). In this instance, you should just select either a screw or a threaded bolt. Bolts have flat heads with no openings for a screwdriver of any kind, in case you were not sure of the difference. If you already know that you are dealing with a metric screw or bolt, use the metric thread gauge. Otherwise have both an Imperial (i.e., standard measurement, not metric) thread gauge and a metric thread gauge handy.
Examine How Far Apart the Screw/Bolt Threads Are
A bit of "guestimation" is needed here. You will have to look at the threads on the fastener you chose and guess at how far apart the winding threads are. It will help you select and flip open the thread gauge instruments that most closely match the distance between each winding loop of the threads.
Select the Pitches of Your Gauges That Look Like They Might Be a Good Fit
Each pitch tool you flip open on the thread gauges has several notches interspersed with points. The points fit into the grooves between the fastener threads, while the notches fit with raised edges of the threads on bolts and screws. Test the pitch tools that you think will fit with your bolt screw. The one pitch tool that most closely fits with the threads without being too big/wide or too small/narrow is the one that will tell you exactly what size and type of screw/bolt and thread pitch you are dealing with. Then if you need more of that particular bolt or screw, you know exactly what to purchase at the hardware store. You can also use these gauges to sort out and organize dozens of fasteners that you have thrown in a junk drawer.
For more information, talk to companies like WESTport.