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lag screw
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Illustration showing seven types of screws and screw heads in a row, including a cap screw, machine screw with oval head, setscrew with hollow head, self-tapping screw, flat-head wood screw, machine screw with Phillips head, and lag screw, each labeled beneath.
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lag screw

machine component
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Illustration showing seven types of screws and screw heads in a row, including a cap screw, machine screw with oval head, setscrew with hollow head, self-tapping screw, flat-head wood screw, machine screw with Phillips head, and lag screw, each labeled beneath.
Screws and screw heads Screws and screw heads (A) Cap screw, (B) machine screw with oval head, (C) setscrew with hollow head, (D) self-tapping screw, (E) flat-head wood screw, (F) machine screw with Phillips head, (G) lag screw.

A lag screw, also known as a lag bolt, is a type of screw characterized by a wrench head and threads designed for wood, terminating in a point. These screws are used to fasten or join materials, particularly wood. The term originates from their historical use in securing lags (large pieces of wood) to drums or cylinders.12

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