Screws/BoltsΒΆ
Screws and bolts are used to hold together to parts by pressing them together and sometimes threading directly into one of the parts. The two terms are often used in an ambiguous way as the distinction is poorly defined. There is even a US Customs document “Distinguishing Bolts from Screws” Both are threaded fasteners, but distinctions are often made based on the size and use of the fastener. There are many types of screws listed on the Wikipedia screw page
Screws and bolts hold firmly against shear and tension on the parts. Some shoulder bolts or most long bolts have an unthreaded section to reduce the fretting of unthreaded sections of parts and/or allow a pivot point. Bolts are made in a variety of grades that represent different strengths. Markings on the head indicate the grade and can be looked up in a grade table
It is common to use screws and bolts with buts for parts with a clear-fit hole. Washers are used to distribute the load and reduce surface deformation. Locking washers prevent the assembly from loosening with vibration and use. Compounds such as Loctite are also often used to lock threaded fasteners.
Overview of Screws and Bolts:
Nuts and Washers:
Thread Locking: