British Standard Pipe (BSP) has been used as a standard in plumbing and pipe fittings. There are two types of BSP Thread available. One is Parallel threads or we can say Straight threads. The second one is the Taper Thread.
BSP is BRITISH STANDARD PIPE THREAD– Also known as Whitworth 55° Thread Form.
BSPT is BRITISH STANDARD PIPE TAPER THREAD – Thread form per AS 1722.1, BS 21, ISO 7.
BSPP is BRITISH STANDARD PIPE PARALLEL THREAD – Thread form per AS 1722.2, ISO 228.
British Standard Pipe Parallel thread (BSPP) is also known as British Standard Pipe Fitting thread (BSPF) and British Standard Pipe Mechanical thread (BSPM). Female and Male threads are both parallel.
BSPP thread used where a pressure-tight joint is achieved by the compression of soft material (such as an o-ring seal or a washer) between the end face of the male thread and a socket or nipple face, with the tightening of a backnut.
British Standard Pipe Taper thread (BSPT) whose diameter increases or decreases along the length of the thread.
BSPT thread is used where pressure-tightness is made through the mating of two threads together. International standards require all Female thread is parallel and male thread is tapered. The female thread can also be tapered but this is not common.
TPI stands for Threads Per Inch, which means the total number of threads per inch measured along the length of a fastener. TPI is used only with American fasteners. Metric Fasteners use a thread Pitch. In general, smaller fasteners have finer threads, so the thread count is higher.
The thread pitch is the distance between threads expressed in millimeters. In general, smaller fasteners have finer threads, so they have a lower thread pitch.
| Size | Pitch | External Thread OD | Internal Thread ID | ||
|---|---|---|---|---|---|
| inch | TPI | mm | inch | mm | inch |
| 1/8 | 28 | 9.6 | 0.38 | 8.6 | 0.34 |
| 1/4 | 19 | 13.0 | 0.51 | 11.9 | 0.47 |
| 3/8 | 19 | 16.5 | 0.65 | 15.2 | 0.6 |
| 1/2 | 14 | 20.8 | 0.82 | 19.1 | 0.75 |
| 5/8 | 14 | 22.8 | 0.9 | 20.8 | 0.82 |
| 3/4 | 14 | 26.3 | 1.04 | 24.6 | 0.97 |
| 1 | 11 | 31.1 | 1.3 | 30.7 | 1.21 |
| 1-1/4 | 11 | 41.8 | 1.64 | 39.4 | 1.55 |
| 1-1/2 | 11 | 47.7 | 1.88 | 45.5 | 1.79 |
| 2 | 11 | 59.5 | 2.34 | 57.4 | 2.26 |
| 2-1/2 | 11 | 75.1 | 2.95 | 72.6 | 2.86 |
| 3 | 11 | 87.9 | 3.46 | 85.4 | 3.36 |
| Size | Pitch | External Thread OD | Internal Thread ID | ||
|---|---|---|---|---|---|
| inch | TPI | mm | inch | mm | inch |
| 1/8 | 28 | 9.5 | 0.37 | 8.4 | 0.33 |
| 1/4 | 19 | 12.8 | 0.5 | 11.2 | 0.44 |
| 3/8 | 19 | 16.3 | 0.64 | 14.7 | 0.59 |
| 1/2 | 14 | 20.4 | 0.8 | 18.3 | 0.72 |
| 5/8 | 14 | 22.5 | 0.89 | 20.6 | 0.81 |
| 3/4 | 14 | 25.9 | 1.02 | 23.9 | 0.94 |
| 1 | 11 | 32.6 | 1.28 | 29.7 | 1.17 |
| 1-1/4 | 11 | 41.1 | 1.62 | 38.6 | 1.52 |
| 1-1/2 | 11 | 47.0 | 1.85 | 44.5 | 1.75 |
| 2 | 11 | 58.6 | 2.31 | 56.4 | 2.22 |
| 2-1/2 | 11 | 74.1 | 2.92 | 71.9 | 2.83 |
| 3 | 11 | 86.6 | 3.41 | 84.6 | 3.33 |
