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Bolts and Screws061604-002

2350 Campbell Road

FAX: 937-498-7544 Admin.

Sidney, OH 45365-9573

FAX: 937-498-4911 Sales

Bolts and Screws

A mechanical joint must provide sufficient flange pressure to create and maintain a seal. Bolts

or screws are the fasteners commonly used to give the clamping load that provides the

pressure at the flanges.

Bolts and screws are among the many types of threaded devices referred to collectively as

fasteners. There is some overlap between the definitions of bolts and screws. Generally, if the

fastener is designed for use with a nut, and if it is tightened by ap plying a torque to the nut, then

the fastener is a bolt. If it is designed for insertion into a hole with internal threads (as in an

engine block), and if it is tightened by applying a torque to its head, then the fastener is a screw.

Studs are headless fasteners or threaded rods. In the chemical industry, where standard pipe

flanges are usual, through bolts are used almost exclusively. In other industries, most flat-faced

flanges are clamped together with tap bolts or cap screws.

In the above figure, the arrows point to the root and the crest of the threads. The pitch of the

thread is the distance from the crest of one thread to the crest of the next thread. This

measurement is used to determine the number of threads per inch, or millimeters per thread,

data that are usually supplied by the fastener manufacturer. The one most frequently used term

in designating the size of a bolt or screw fastener is its nominal diameter.