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Terms Used for Screw Threads

Some General Terms Used for Screw Threads

Thread Pitch: this is the distance between threads. eg the distance between the thread crests might be 1 mm vs 1.5mm. Thread pitch is the main difference between NPT and BSP standards.

Straight vs Tapered (aka Parallel vs Dynamic) - where the diameter/thickness, starts wide and becomes thinner.

Thread Forms: The shape/form of the Thread Peaks and Thread Valleys.

Thread Peaks (aka Thread Crests) - ie the tips / top edges of the threads.

Thread Valleys (aka roots) - ie the lowest points between the threads.

Thread Flanks - the surface of the thread between the valleys and the Peaks. the angle of these is the “thread flank angle”.

Callipers - a measuring tool to determine diameter.

Diameter - the full width of a circle eg the line that goes through the middle of a circle if you were to cut it in half.

Outside Diameter - eg the outside edge-to-edge of a pipe or adapter.
Inside diameter - eg the size of the hole inside a pipe / the “borehole”.

A Thread / Pitch Gauge - a measuring tool that gives you the thread pitch etc (see above).


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