written, compiled and edited by Bernard Martin

Class of fit for a cutting tap refers to the specific tolerance or fit that is desired between the threads of the tap and the threads of the hole it is being used to create. In other words, it defines how tightly or loosely the threads should mesh together.

The class of fit is typically expressed using a combination of letters and numbers. The most commonly used standards for class of fit are the Unified Thread Standard (UTS) and the ISO metric thread standard. In the UTS, the class of fit is denoted by a combination of a letter and a number, such as 2B, 3A, etc. In the ISO metric thread standard, it is represented by a combination of a letter and a number, such as 6g, 4h, etc.

For cutting taps, the class of fit is usually specified based on the intended application and the level of precision required. The class of fit can affect factors like the ease of assembly, the strength of the threaded connection, and the ability to engage the threads smoothly during tapping.

A classification system exists for ease of manufacture and interchangeability of fabricated threaded items. Most, but certainly not all, threaded items are made to a UTS classification standard. This system is analogous to the fits used with assembled parts.

• Class 1 threads are loose fit, intended for ease of assembly or use in a dirty environment.
• Class 2 threads are free fit, and the most common. They are designed to maximize strength considering typical machine shop capability and machine practice.
• Class 3 threads are medium fit, still quite common and used for closer tolerances on high quality work.
• Class 4 threads previously designated a close fit for even tighter tolerances, but this classification is now obsolete.
• Class 5 fit is an interference thread, requiring the use of a wrench for turning. These can be seen in applications like spring shackles on an automobile.

The letter suffix "A" or "B" denotes whether the threads are external or internal, respectively. Classes 1A, 2A, 3A apply to external threads; Classes 1B, 2B, 3B apply to internal threads

Here are some common classes of fit for cutting taps:

1. Class 2B (UTS) or 6H (ISO metric): This is a standard fit for most general-purpose applications. It provides a balance between ease of assembly and thread engagement.
2. Class 3B (UTS) or 6HX (ISO metric): This is a tighter fit than Class 2B or 6H and is used when a higher level of thread precision and engagement is required.
3. Class 2A (UTS) or 6g (ISO metric): This is a loose fit that is often used for applications where ease of assembly and disassembly are important, such as with interchangeable parts.
4. Class 3A (UTS) or 6HX (ISO metric): This is a tighter fit than Class 2A or 6g and is used in applications where a higher level of precision is required.

The choice of class of fit should be made based on the specific requirements of the project, taking into consideration factors like material type, thread size, intended use, and the desired level of thread engagement. It's important to consult relevant standards and guidelines to ensure that the chosen class of fit is appropriate for the application.
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The standard designation for a UTS thread is a number indicating the nominal (major) diameter of the thread, followed by the pitch measured in threads per inch. For diameters smaller than 1⁄4 inch, the diameter is indicated by an integer number defined in the standard; for all other diameters, the inch figure is given.

This number pair is optionally followed by the letters UNC, UNF or UNEF (Unified) if the diameter-pitch combination is from the coarse, fine, or extra fineseries, and may also be followed by a tolerance class.
Example: #6-32 UNC 2B (major diameter: 0.1380 inch, pitch: 32 tpi)

Browne & Co has been appointed as Regaional Managers for Regal Cutting Tools.  They will be responsibilve for distributor and technical support for the Kentucky, Ohio, and Western Pennsylvania market areas.

Regal Cutting Tools has been manufacturing world-class cutting tools since 1955  Regal offers a high performance SuperTuf series of taps for the demanding difficult to machine materials.

Regal also manufactures special taps from blanks with as little as 24 hour notice.

According to Dave Browne, President of Browne & Co, "Regal Cutting Tools. is a well established and trusted brand within the metalcutting industry. Their full line of taps as well as their tap specials capabilities really compliment our product mix and fills an area we have pretty deep experience in but didn't have a product to recommend.  We're really looking forward to working with our customers and running these tools!"

Almost a year ago, Allen Benjamin, which has been a part of North American Tool,  was purchased by GWS Tool Group. GWS Tool Group is a US-based, vertically integrated manufacturer of highly engineered custom, standard, and modified standard cutting tools, primarily servicing the aerospace and defense, power generation, automotive and medical sectors. GWS Tool Group has acquired multiple businesses in the course of its growth which now serves as the respective manufacturing divisions for the Company.  

Just because there is a new owner, doesn't mean that the quality of an Allen Benjamin Tap has changed! 

If you’re in the market for high tensile strength carbide taps and metric taps, we can assure you that you’re in the right place. Not only is Allen Benjamin a leading supplier of the industry’s most durable, longest lasting carbide taps, we offer our customers the convenience of ordering online. In this day and age, we believe that quick access and top-notch customer services are critical.

In today’s post, we’re going to look at why it is beneficial to order your carbide taps from Allen Benjamin.

Quality
Allen Benjamin carbide taps are highly efficient when tapping abrasive metals such as aluminum, non-ferrous metals, and exotic materials. With a much higher tensile strength than standard taps, their high-quality carbide taps can withstand the rigorous demands of your application.

Selection
Allen Benjamin offers a staggering range      of carbide taps, metric taps, HSSE taps, tapping fluid, extensions, and more. If it’s taps that you are looking for, you can be confident that they’ve got them and have them ready for delivery.

Service
Allen Benjamin guarantees that all of their products will be the absolute best quality, within standard tolerances and dimensions, and consistent with application specifications. If their goods don’t meet your needs, you can contact us for a return authorization.

At Allen Benjamin, they take pride in offering the industry’s best taps. But, more importantly, they aim to provide our customers with access to a simpler, faster way to order their operation’s critical parts, supplies, and components.

If you’ve been searching for a supplier that will meet your needs and rise to meet your challenges contact us today!

How can you optimize a tap's chamfer based on your application?

Although North American Tool/ GWS  stocks many common special taps with standard chamfer lengths, they can design and manufacture a special tap for your application.

​Optimizing the chamfer results in, longer tap life, reduced tapping torque, better finish, and make the difference between success and failure.

As most of you know, the chamfer is the tapered section on the front of the tap. It includes the length, angle, radial relief, and point diameter.

​As the tap rotates and advances forward, each succeeding chamfered tooth enters the drilled hole and takes deeper and deeper cuts until the first full thread on the tap completes producing a full thread in the part. The balance of the tap’s threads within the length beyond the chamfer, do not do any cutting and just goes for the ride.
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Increasing the total number of chamfered teeth cutting, can increase tap life exponentially.

​The example above shows that a standard plug chamfer (3 to 5 threads) length, so on a 4 fluted tap, it will range between 12 to 20 cutting teeth. Because North American Tool/ GWS understands more is better, they make it a point to manufacture our taps with a chamfer length closer to maximum length, in this case, 5 threads. This is also true for the other standard chamfer lengths Bottom, Semi Bottom, and Taper. 

Although more is better, you may be limited to the length of chamfer due to the job requirements. We should also note that the incomplete threads created and left in the part by the chamfer are not too full thread height and will cause assembly interference, therefore they are not considered part of the required thread length.

As for manufactured specials, knowing your application requirements is necessary for us to design a tap that optimizes performance. For chamfer design, North American Tool/ GWS would need to know, tap drill size, tap drill depth, and full thread length requirement.

Knowing the tap drill size allows us to grind a chamfer with a point diameter that permits the tap to start cutting within the first half thread of entry. Because there are many factors that go into determining a tap drill size, there can be a relatively wide range of diameters. If the chamfer point diameter is smaller than the tap drill diameter, then the tap may not start cutting until the second chamfer tooth or beyond.

Using the same 4 flute, plug tap from the example above, in an application with a tap drill size larger than the chamfer point diameter, such that the tap does not start cutting till the 2nd chamfer tooth, will have a reduction in cutting teeth by 6 (1.5 threads X 4 flutes), or 30%. If the application is such that only a bottom chamfer (1 to 2 threads) can be used, and it is ground to the maximum length of 2 threads it will result in a reduction of cutting teeth from 8 (2 threads X 4 flutes) to 6 (1.5 threads X 4 flutes) or 75%.

Knowing the tap drill depth and full thread length requirement also allows us to design the maximum length chamfer for your application. This may take into consideration the overspin of the machine spindle, or room at the bottom of a blind hole so the tap does not run into any chips that may have made their way to the bottom.

Although the information presented may be confusing, hopefully we have explained the importance of the chamfer, and the many considerations that go into its proper design.

So, if you are ready to increase tap life, reduced tapping torque, improve the finish, and make the difference between success and failure, give us a call with your application requirements.