Have A Question About Steps In Pipe Thread Ring & Plug Gages?

No Steps In The Gage?

Pipe thread ring gages (NPT NPTF & ANPT) are made with no steps, that is true unless specifically requested at the time of purchase. That is also true for pipe thread ring gages made to BSPT, BS-21, & System-A. All of these pipe thread ring gages are used by counting the number of turns onto the threaded part you are inspecting. The user is to count, plus / minus one turn, of the part / product from the small end of the pipe thread ring gage.

One-Step In The Gage?

 
This is one of the most confused step counts of them all! Be very careful at this step because a two-step pipe thread plug gage could be confused with a one-step pipe thread plug gage. NPT, NPTF, & ANPT pipe thread plug gages are made with one-step, unless specifically requested at the time of purchase. There is a chance that the step is marked “BASIC” but this is not very likely. You will use the pipe thread plug gage by counting the number of turns into the threaded part / product. The user is to count, plus / minus one turn, of the part / product from the step machined into the pipe thread plug gage.

Two-Steps In The Gage?

You will see this step count a lot if you purchase gages outside of the US. If you have a BSPT pipe thread gage and it has two-steps, it is designated as System-B. To make it simple, a two-step pipe thread gage is a Go / No Go gage for a couple reasons. The first is that the part must "Go" past the first step. The next is that the pipe thread gage should "No Go" past the end of the pipe thread gage which is the second step. The pipe thread gage steps could be marked with any of the following: “+” & “-” OR “MIN” & “MAX”. In the US a three step pipe thread gage is much more commonly used, vs the two-step pipe thread gage. The two-step pipe thread gage does have an advantage though, this is that it removes a lot of guesswork from the machine operator or the person using the pipe thread gage.

Three-Steps In The Gage?

A three-step pipe thread gage is very similar to a two-step pipe thread gage with the addition of a "BASIC" step. This kind of pipe thread gage is very common in US. If it is a pipe thread plug gage, and a three-step is requested by the customer, a gage manufacturer can remove a standard one-step pip thread plug gage from stock and add the other two steps to the pipe thread plug gage, taking it from a one-step to a three-step. Many will notice that the three-step pipe thread plug gage is the preferred gage in the US by both the manufacturer and the consumer. This is because the cost of modifying the stocked gage is much less and much faster when it comes to shipping, vs the cost of making a new two-step pipe thread plug gage or a four-step pipe thread plug gage. If you are looking at a pipe thread ring gage, a three-step pipe thread ring gage is much less common. Pipe thread ring gages can be made as three-steps, but that is not typically done because that is much more expensive. This is because the gage manufacturer cannot easily modify a standard no-step pipe thread ring gage into a three-step pipe thread ring gage. Most gage manufacturers produce a three-step pipe thread ring gage as a "special", using specially made pipe thread ring gage blanks. The cost of making the pipe thread ring gage special can be a bit higher than the cost of purchasing a no-step pipe thread ring gage. In addition, the lead-time could be extended to 6 weeks. But you can always call for a quote! The three steps on a pipe thread ring gage may be marked: “MAX”, “BASIC”, & “MIN”. Similar to the two-step pipe thread ring gage, the three-step pipe thread ring gage is a Go / No Go pipe thread ring gage. This is because the part must "Go" past the first step and "No Go" past the end of the pipe thread ring gage, which is the second step on the pipe thread ring gage. The "BASIC" step, on the pipe thread ring gage, should be the target for a part. This is in the middle of the tolerance range of the pipe thread ring gage. Many think that the small additional cost of a three-step pipe thread plug gage will pay for itself on the production floor. It does this by removing a large majority of the guesswork from the machine operator or inspector that is using the pipe thread gage.

Four-Steps In The Gage? 

A four-step L-1 (L1) pipe thread gage can be used to facilitate the use of 6-step crest check pipe thread gages and root check pipe thread gages. A four-step pipe thread gage is most likely only used for ANPT or NPTF. This is where the additional six-step pipe thread gages,root-check pipe thread gages, and crest-check pipe thread gages, are required. In order to use a six-step pipe thread gage, the user / inspector must have knowledge or the ability to read a L1 pipe thread gage. This is done in thirds of the product / part tolerance. The four-step pipe thread gage design makes the "thirds" of tolerance easily identifiable. This makes reading the additional pipe thread gages much more accurate and doable. The steps on these pipe thread gages are numbered: 1, 2, 3, & 4. Between step-1 and Step-2 is the maximum range on the pipe thread gage. Between step-2 and step-3 is the basic range on the pipe thread gage. Between step-3 and step-4 is the minimum range on the pipe thread gage.

Six-Steps In The Gage?

A six-step pipe thread gage is used for ANPT and NPTF, and is used when testing the root (root-check pipe thread gage) or crest (crest-check pipe thread gage) of the product / part threads. The six steps, in the pipe thread gage, are needed because of the three zones of the pipe thread gage are overlapping. That overlap in the pipe thread gage requires the two additional steps to identify / call out the same three zones as found in the four-step pipe thread gages. Checking the root and the crest of a product / part threads is critical for NPTF. This is because the thread accomplishes a dry-seal by crushing the root and crest of the mating threads together, in a wrench-tight assembly. If the root or the crest is not within tolerance, then the dry-seal will not occur and some potentially hazardous leakage could happen. The six steps of the pipe thread gages are marked: MX, MXT, B, BT, MN, & MNT. 

Disclaimer: To the best of our knowledge, the information contained herein is accurate and reliable as of the date of publication; however, we do not assume any liability whatsoever for the accuracy and completeness of the above information. M & J Tooling LLC makes no warranties which extend beyond the description contained herein. Any information given in this statement does not constitute any warranty of merchant ability or fitness for a particular use. It is the customers' responsibility to fact check and confirm any of the above information in order to satisfy themselves as to the suitability of the products to their particular purpose.