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self-drilling screw Tek screw: Similar to a sheet metal screw, but it has a drill-shaped point to cut through the substrate to eliminate the need for drilling a pilot hole. Designed for use in soft steel or other metals. The points are numbered from 1 through 5; the larger the number, the thicker metal it can go through without a pilot hole.
A self-tapping screw is a screw that can tap its own hole as it is driven into the material. More narrowly, self-tapping is used only to describe a specific type of thread-cutting screw intended to produce a thread in relatively soft material or sheet materials, excluding wood screws .
Tapcon screws are a popular anchor that stands for self tapping (self threading) concrete screw. Larger diameter screws are referred to as LDT's. This type of fastener requires a pre-drilled hole—using a Tapcon drillbit—and are then screwed into the hole using a standard hex or phillips bit. These screws are often blue, white, or stainless ...
Example (inch, coarse): For size 7 ⁄ 16 (this is the diameter of the intended screw in fraction form)-14 (this is the number of threads per inch; 14 is considered coarse), 0.437 in × 0.85 = 0.371 in. Therefore, a size 7 ⁄ 16 screw (7 ⁄ 16 ≈ 0.437) with 14 threads per inch (coarse) needs a tap drill with a diameter of about 0.371 inches.
Self-tapping pocket screws are used for pocket hole joints. Pocket screws are generally more expensive, but they are needed for a tight, strong joint. Pocket screws have a wide washer head to spread the load for a firm bond, and prevent screwing too far into the joint and cracking the wood.
Self-tapping sheet metal screws are available in aluminum alloys, but cadmium-plated steel screws are employed more commonly to obtain higher shear strength and driveability. Alloy 2024-T4 with an anodic coating is standard for aluminum screws, bolts, and nuts made to military specifications.
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