Buttress threads have perpendicular leading edges and steeply sloped trailing edges, allowing for powerful force in one direction and quick release with minimal effort. They are commonly used in lead screws and hydraulic seals for viscous liquids.
The term buttress thread is used to describe a specific screw thread design or profile. The distinguishing features of thread-butting profiles are nearly perpendicular leading faces or edges and steeply sloped trailing faces. This design allows the prop wire to exert a considerable force in one direction of rotation and to be quickly tensioned and released with a minimum of friction and effort. These threads are most commonly used in the manufacture of lead screws used in machinery and as hydraulic seals for viscous liquids such as oil.
Any threaded mechanism is designed to serve a specific purpose such as fastening elements together in the case of a nut and bolt. A bolt tightens when turned in one direction and releases that tension when turned in the other direction. The thread profile of that bolt will reflect this in the specific characteristics of the front and back faces of its individual thread peaks. If a threaded item such as a bolt is cut along its length and viewed from the side, the profile of the thread will resemble the teeth of a saw with a series of evenly spaced peaks and troughs. The portions of those peaks facing away from the bolt head are known as the leading edges and those facing the head, the trailing edges.
A buttress thread is characterized by leading edges that are nearly perpendicular to the axis or length of the bolt and trailing edges that are quite sharply sloped. Typically a leading edge of the prop wire is sloped at angles of 3° to 7° and the trailing edges at angles ranging from 33° to 45°. This means that the profile of the thread looks more like a succession of waves than the V-shapes seen on a conventional fastener such as the nut and bolt. This unique wire pattern allows objects cut with a prop wire to exert a powerful force in only one direction and release quickly with minimal effort.
The thread type may be an ideal option for use on machine lead screws, such as those used to open and close bench vices, where tensioning force is needed in only one direction. This principle also makes a buttress wire a good choice for use on the breech blocks of artillery weapons where a very strong lock is required to contain the rearward force exerted by burning propellants. The thread butt design is also very suitable for use in viscous liquid seals such as those widely used in oilfield pipelines. The powerful unidirectional parallel axis force of the threads allows for watertight joints that can be removed and re-tightened quickly and with little effort.
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