The next time you unscrew the cap from your tube of toothpaste, take a look at the threads. They are quite likely Buttress threads. Have you used an adjustable wrench lately? Look at the thumb-screw. Buttress! All this time, right under your nose, was a thread-form that most people think, or know very little about.
Synonyms for “buttress” include; strengthen, reinforce, fortify, and support. The unique geometry of a buttress thread-form fulfills that requirement.
This thread-form is designed to stand up to a heavy axial load in one direction. This enables the thread to “push” or “pull” depending on the orientation of the “pressure” flank. It also allows the thread to resist great axial pressure from one direction. Developed sometime in the late 1800’s, early use was seen in the design of breach-lock mechanisms for artillery. As aviation developed, buttress threads were utilized on propeller hubs to withstand extreme axial loads. Vises and presses have always been an appropriate application where axial force is applied in one direction. Ideal for heavy lifting, buttress threads are frequently used for the lead screws in jack stands. More recently, this thread design has seen use in dental implants, as biting force exerts extreme force in one direction.
Standardization of the thread-form didn’t occur until the early 1940’s, when it was reviewed as needed for the war effort. For those familiar only with a more recent history, that would be World War II. At an American-British-Canadian Conference in New York in 1943, it was decided that Buttress threads would be discussed, and a basic profile would be established. It wasn’t until a meeting of the same group in London in 1944, that an agreement was reached to assign a standard Buttress form with a 7-degree pressure-flank angle, and a trailing clearance flank angle of 45 degrees. “Special” Buttress thread angles are not uncommon in spite of the accepted standards. As it was before the standard was assigned, each application may be treated individually, with the buttress form dependent on the designer and manufacturing capabilities.
When ordering a Buttress tap, it will be assumed to be the “standard” geometry unless alternate information is shared. “Push” or “pull” use will be need to be defined. Application details like material, depth-of-thread, through or blind hole are always required to engineer the proper geometry for any tap, including this one. If a special thread profile (leading and trailing flank angles) is specified, we will require a part print for confirmation before quoting or manufacture.