Well drilling pipe often has this type of thread, and I have also seen cannon breeches with interrupted steep tapered threads. Formerly known as the Briggs Thread, the pipe thread used in America is the American National Standard Taper Pipe Thread. Britain uses the British Standard Pipe Thread, which has the Whitworth thread form. The term ‘stub ‘ means a shallower than usual thread. There is also a 60 Degree Stub Thread of vee form for applications such as tubing, where a normal depth thread would seriously weaken the thin wall.Coarse threads on bolts must be cut deeper into the bolt material than fine threads, and the root diameter of the bolt is smaller, and thus weaker. A disadvantage of multiple threads is that the high lead angle thread tends to loosen easily with vibration. Some ‘deck’ screws used in wood have multiple threads for fast insertion.Left hand threads can be useful for applications such as the wheel nuts on the left sides of automobiles, where the rotation of the wheels tends to keep the nuts from unscrewing. Major Diameter: The largest diameter. The ‘tap drill‘ leaves the correct amount of metal for the threads. These fluteless taps must have exactly the right size hole drilled first, and must be properly lubricated. The United States standard uses inches and the European standard uses millimeters. Many of these special threads are still in use today, and the specifications of them can be found in Machinery’s Handbook and other mechanical reference texts.In the American and English systems, threads are typically specified by the major diameter and the threads per inch: for example, 5/8 inch-11. This is equal to one over the pitch (1/P). Multiple threads screw in rapidly: my fountain pen cap has four starts and tightens with only 3/4 of a turn. In certain metals like non magnetic stainless steel, and copper alloys, that work-harden rapidly, fluteless taps produce threads that are stronger and harder than the parent metal.Threads are wonderful things that help us daily, and I hope this article may increase your knowledge and appreciation of them.Acme threads are easier to cut, and can carry high loads. So they are very popular for reinforcing or repairing threaded joints. - Tolerance classes of 1A, 2A and 3A for bolts and 1B, 2B and 3B for nuts - Thread size from 0.0600 inch to 2 inches These tools are used to cut threads in holes.Years ago some interesting size variations based on standard thread systems were developed. These sizes are obsolete, but if you are working on older items you may find such a set very useful. Joseph Whitworth was years ahead in his design having radiused thread roots. Having threads that are slightly larger than standard allows easier repairs when threaded holes become worn. My friend Kim Pisor gave me set of old threading dies that belonged to Jack Renault, the brilliant machinist and founder of Gabilan Iron and Machine in Salinas, California. Some threads are ground “from the solid” in hardened metal, and others are roughed in by other means, hardened, then ground to final form and pitch. Here in our town the saddlemaker uses Landis, and Champion sewing machines, and many of the screws and bolts on them have unusual sizes and pitches. When he needs new screws and bolts on the machines, I often have to use my lathe gearing to cut the odd pitches.Vee form threads are the most common in fasteners today, but there are other thread shapes that have advantages for certain applications. The Whitworth form is greatly superior in fatigue strength, and we will discuss why a bit later. There are many niche industries that have long used special thread standards for things like watches, microscope lenses, power pole insulators, fire hose couplings, compressed gas fittings, etc. Only in Class 2A threads is the allowance available to accommodate coatings. There are a variety of modern screws designed for wood and particleboard, having thin shanks and aggressive self tapping thread designs that minimize splitting, even when holes are not pre-drilled.For turnbuckles and certain clamps, left hand threads on one end of the screw, and right hand threads on the other, will draw the parts together. You have probably noticed that every trade has its secret language, and it will be helpful now to list some of the special terms used when speaking about threads. after the Society of Automotive Engineers, and its wide use in automotive applications).Buttress threads have a square or almost square thrust face and are angled on the back side. (Graphic courtesy of www.educationdiscussion.com)The British use another system for small screw sizes; called the British Association Thread. The grooves in the dies have the shape of the thread profile, and press the threads into the metal without removing any chips. The Lowenherz Thread uses 53 degrees 8 minutes, and the Swiss Thury and the British Association Threads use 47 - 1/2 degrees. Nominal Thread Size: Covered Range: 0-80 UNF to ¼-56 UNS: Nominal thread sizes from 0-80 UNF to ¼-56 UNS 5/16-18 UNC to 9/16 -32 UN: Nominal thread sizes from 5/16-18 UNC to 9/16 -32 UN In the early 1900’s many American companies produced threading tools that were 1/64 inch or 1/32 inch larger than, and also smaller than, the National Standard Thread size.