Threads

Threads are wrapped inclined planes that let us fasten parts together. There are many thread standards, the most common being the Unified Thread Standard coarse and fine variants (UNC and UNF). There are also metric thread standards and a smattering of speciality threads.

Threads are defined by their handedness (tightens in the right or left direction), their form (generally triangular), angle (generally sixty degrees), pitch (distance between thread highs), starts (where they can be engaged), diameters (major and minor), and lead (how much linear axial distance one turn of threads covers).

Consult a thread table or reference guide to learn the specifics of a given thread, but for laboratory work, we are generally working with UNC and UNF in the #2-#10 range, but metric is slowly becoming more common place in the US.

Threads can be cut on a lathe or CNC mill, but are most commonly cut in the laboratory with a tap for internal threads and a die for external threads.

Cutting internal threads:

Cutting external threads:

Unknown threads can be identified using a thread pitch gauge and calipers: