Inch sized fasteners and more

Overview thread types

The world of threads encompasses a variety of types, each suitable for different applications. At Fürniss GmbH, you will find a wide selection of common thread types, from American Unified Threads such as UNC, UNF, and UNEF to British Standard Threads like BSW and BSF. For special purposes, there is the NPT pipe thread, which provides a self-sealing connection, and the R thread, available in both tapered and cylindrical forms. Each thread type has its own unique characteristics and applications. For more information and detailed thread tables, please refer to the linked subpages.

UNC - Unified Coarse Thread Series

American standard coarse thread. The old designation NC is comparable with the metric thread. The new designation UNC is comparable to the ISO metric thread. NC and UNC threads are interchangeable, corresponding to the metric and iso-metric threads.

UNF - Unified National Fine Thread Series = fine pitch thread.

Same design as UNC. UNC and UNF threads are the thread selection for commercial screws and nuts.

UNEF: Unified Extra Fine Thread Series

Unified Extra Fine Thread Series is an extra fine thread used for special purposes.

NPT - National Pipe Thread

American pipe thread for self-sealing connections (tapered), with sealant.

BSW - British Standard Whitworth Coarse Thread Series (cylindrical)

The most common thread in England. Corresponds to the metric thread in its type of use.

BSF - British Standard Fine Thread Series (cylindrical)

BSW and BSF are the thread selection for standard screws and nuts. A fine thread which is widely used in the British machine tool industry but is displaced by the American UNF thread.

R - Tapered threads

Tapered threads according to EN 10226 are referred to as “metal-sealing.” A cylindrical internal thread is denoted by “Rp…,” a tapered or conical external thread by “R…,” and a tapered or conical internal thread by “Rc….” The nominal diameter of the tapered thread corresponds to that of the cylindrical mating thread after a few turns. With further tightening, the threads jam into each other, creating a metal seal. However, such “R threads” are additionally treated with sealing materials like Teflon or hemp before screwing to fill the remaining gaps.

BA - British Association Standard Thread.

The BA thread is commonly used for watches and instruments. However, the metric ISO thread and the ISO fine thread are increasingly displacing it.

R - Cylindrical threads

Cylindrical threads according to ISO 228-1 (designated with “G…,” previously there was a risk of confusion as the thread was also designated with “R”) are not metal-sealing. They are provided with an annular seal (round ring, O-ring), which is more reliable than simple wrapping with Teflon or hemp; however, they require machine-made flat recesses to ensure sealing. Cylindrical threads cannot be sealed by tightening. Tapered R external threads can be sealingly screwed into cylindrical G internal threads since both internal threads are cylindrical.