| Machine Screws, also referred to as Machine Bolts, are often used with nuts or driven into tapped holes. They come in a variety of head types and drive styles, but are generally available in smaller sizes. Polyvinylchloride, or PVC, exhibits little or no water absorption, absorbing 0.05% of its weight after 24 hours of exposure to water. Because it is chlorinated, PVC also possesses natural flame retardant qualities. PVC has one of the highest dielectric strengths of plastics, at 1413 volts per millimeter, making it an excellent insulator. PVC possesses average to above average strength compared to other plastics, with a tensile strength of 7450 psi (pounds per square inch) and an impact strength of 5 force pounds (Izod Impact Scale). The primary drawback of PVC is its low melting point temperature of 140 degrees Fahrenheit. Flat head fasteners are designed to fit flush to the surface when used with countersunk holes. Length is measured from the top of the head. Common applications for slotted screws include woodworking, although the drive style is not designed to be used with power drivers. A threaded fastener's size name includes information about the major external diameter, followed by the threads per inch, which indicates if it is coarse or fine. Coarse threads are better when working with brittle materials; they are sturdier and are easier to thread and unthread compared to fine. Coarse threading also allows for thicker coatings and platings. |
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