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A pentalobular screw thread is a form of self-forming thread used for screws. Self-forming screws are used in ductile materials, such as aluminium and plastics. Self-tapping screws are widely used for driving into sheet metal or plastics and forming their own thread. They may be either self-drilling, forming their own hole through unbroken ...
self-tapping machine screw: A self-tapping machine screw is similar to a machine screw, except the lower part of the shank is designed to cut threads as the screw is driven into an untapped hole. The advantage of this screw type over a self-drilling screw is that, if the screw is reinstalled, new threads are not cut as the screw is driven. set bolt
Self-tapping screws can be divided into two classes: [3] those that displace material (especially plastic and thin metal sheets) without removing it, known as "thread-forming" self-tapping screws, and self-tappers with sharp cutting surfaces that remove the material as they are inserted, termed "thread-cutting" self-tapping screws.
By drilling a small pilot hole into the material, into which a screw is then driven, less wedging takes place, thereby reducing the likelihood of the material being split. [2] When a screw is driven without a pilot hole, or with too small a pilot hole, the core of the screw may bind and lead to the screw being broken.
They also allow for the use of angled screw drivers and trim head screws. The socket-headed Robertson screws are self-centering, reduce cam out, stop a power tool when set, and can be removed if painted over or old and rusty. [18] In industry, they speed up production and reduce product damage.
However, some screw mechanisms with a large enough pitch and good lubrication are not self-locking and will overhaul, and a very few, such as a push drill, use the screw in this "backwards" sense, applying axial force to the shaft to turn the screw. Other reasons for the screws to come loose are incorrect design of assembly and external forces ...
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In order for the screws to be able to drill, cut and tap into other materials like steel, the drill point and the forming threads must be harder than the material(s) that it is drilling into. However, if the whole screw is uniformly hard, it will become very brittle and it will break easily. This is overcome by ensuring that only the surface is ...