Thread type: BSB - British Standard Brass Thread

The thread shown in the BSB thread table is a special form with a fixed pitch. BSB stands for British Standard Brass, where Brass is the English word for brass. It is therefore a thread specifically for brass pipes. Despite the name, the thread from the BSB thread table does not belong to the British Standards (BS), the collection of standards of the British Standards Institution (BSI). However, it is a thread type that is based on the British Standard Whitworth (BSW) and has a corresponding 55° flank angle and is also an imperial thread.

As can be seen from the BSB thread table, this type of thread is a thread with a fixed pitch. As is usual with inch threads, the pitch in the BSB thread table is given in threads per inch and is constant at 26, regardless of the thread size. This is due to the fact that brass tubes, for which this special thread is used exclusively, have a barely variable wall thickness. This means that the thickness of the material does not increase in relation to the circumference of the pipe, but remains more or less the same. Therefore, the pitch of the thread used must also be constant in order to prevent the thread depth from no longer being able to be absorbed by the material above a certain level. An optimum value of 26 threads per inch has been established, as you can see in the BSB thread table.  

The BSB thread table includes eleven thread sizes between 1/8" and 1 1/2", which are matched to the common sizes of the brass pipes used. The thread designation is derived from the abbreviation BSB and the outside diameter in inches. We have also included the core hole diameter in mm in our BSB thread table. You will also find a conversion of the outer diameter in mm in the BOD thread table, as well as information on the pitch in threads per inch and also converted into mm. This value is constant at 26 threads per inch or a pitch of 0.977 mm.

 outside-Ø in Inchoutside-Ø in mmcore hole-Ø in mmThreads 
per Inch
pitch P
in mm
BSB 1/8"1/83,1751,923260,977
BSB 1/4"1/45,5565,098260,977
BSB 3/8"3/89,5258,273260,977
BSB 1/2"1/212,70011,448260,977
BSB 5/8"5/815,87514,369260,977
BSB 3/4"3/419,05017,798260,977
BSB 7/8"7/822,22520,973260,977
BSB 1"125,40024,148260,977
BSB 1 1/8"1.1/228,57527,323260,977
BSB 1 1/4"1.1/431,75030,498260,977
BSB 1 1/2"1.1/238,10036,848260,977

Since brass tubes has a constant wall thickness, independent of the pipe diameter, with a larger pitch (smaller number of TPI), the thread depth would increase. This would lead to the reduction of the wall thickness of the pipe.

Cross section of a BSB thread