UN Thread taps or Metric taps – the basics are the same

We had discussed about the tapping techniques involved in one of our previous blogs. We had spoken at length about the different types of handheld taps. The first one that came up for discussion was the taper taps. Now, we shall see the plug taps and the bottoming taps in this article. We shall also look at some of the precautions you should take when you use these taps. The basics are the same for the UN thread taps and the metric taps.

Plug Taps

PLUG taps are like taper taps in that they have tapered threads at the starting end of the tap. The basic difference is that, there are fewer of them, usually the first 3-5 threads, so you get to cut a full thread sooner. Although not as easy to start as a taper tap, they can be used to start a thread. If you can only buy one type of tap, and you’re a patient user, plug taps can be a good choice because they are still easy to start, but they can also form complete threads deeper into a blind hole than a taper tap.

Bottoming taps

BOTTOMING taps have no ground threads at the starting end and are generally used after, and in conjunction with a taper or plug tap. Bottom taps can cut threads to the bottom of blind holes although they do not do well at starting threads.

What is the difference between the UN thread taps and metric taps? The techniques are the same. The only difference is in the usage. The British industries use the metric taps whereas the US-based industries opt for the UN thread taps.

What are threading dies?

You use the threading dies to carve out the external threads. Just as the way the taps cater to the internal threading, the dies cater to external threading. Hand threading dies are generally of two types. ROUND dies are designed to fit in a T-handle while HEX DIE NUTS can be used with regular hand tools. (Wrenches and sockets) Round dies are usually the choice for cutting new threads whereas hex die nuts are commonly used as a chaser to repair existing threads. Round dies also require a holder/handle to use them, whereas hex die nuts do not.

The thread gauges

What type of instrument you need to measure the pitch and the tolerance levels of the threads? In case of the external threads, you need the thread ring gauges whereas the thread plug gauges do the job for you for the internal threads.

The thread gauges work on one of the simplest process in the industry. This is the GO-NOGO principle. Each gauge has two sides, the GO side and the NOGO side. The concerned implement should pass through the GO side of the gauge smoothly without any effort at all. At the same time, it should not go through more than two normal turns from the NOGO side. The implements that pass this test are the ones certified fit for use in the industry.