When you are trying to tap your own screws, for whatever reason, you want to make sure that you are making them so that they will fit in where they need to go and so that you know what size screw you are using. There is one easy way to do that, and that is to measure it with a thread gage. But, what is a thread gage and what does it measure?
A thread gage is a small tool that gets placed up against the screw, and when it is placed on the screw or in anything that is threaded, it tells you what the pitch and the lead of the screw or thread is. It can be used on a single start or double start screw, but it's important to make sure that you measure the correct thread if you are going to measure a double start screw. What are the lead and pitch of a screw?
Lead and pitch are very similar measurements, and in some screws, especially single start screws, they are the same thing. But it isn't a guarantee that they are both the same measurement, so it's important to make sure that they are measured correctly. On a screw, the lead is measured as the distance around the axis that the thread travels when the screw is turned once. The lead is measured on one thread, so in a double start screw, it would have two lead measurements, one for each of the threads.
The pitch of the screw is measured from one point on the ridge of a screw to the next point of the ridge directly over it. It's a vertical measurement, instead of a measurement of distance traveled. Again, like the lead, the pitch needs to be measured for each thread on a screw, so only once on a single start screw and twice on a double start screw. The way that the measurement is used and expressed is different when it comes to imperial versus metric screws.
If you are going to make screws or tap a thread for anything, you need to make sure that you know how that screw is measured. The way to do that is to take advantage of a thread gage. With this gage, you can find out the exact measurements of the screw so that you can use it in whatever purpose you need.