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Threaded Fitting Sizes and Dimensions

Calculate the correct thread pitch and nominal bore size.

If there are six whole threads within the N Distance and if N =- 3/4″ then the calculation is 6 divided by 3/4 which equals 8 TPI (TPI = Thread per Inch)


Example: If the above fitting measurement at X is 1-7/8″ (47.6mm), then the NB Size is 1-1/2″ (38mm)

Nominal Bore(NB)
Pipe Size
Approx. Measurement of
OutsideDiameter of
MALE THREAD
Threads
per inch
Thread Pitch
(Distance between each thread)

thread pitch
Imperial Metric Imperial Metric (TPI) (mm) (inch)
1/8″ BSP (6mm) 9.5mm (3/8″) 28 0.91 0.036
1/8″ NPT (6mm) 9.5mm (3/8″) 27 0.94 0.037
1/4″ BSP (8mm) 12.7mm (1/2″) 19 1.34 0.053
1/4″ NPT (8mm) 12.7mm (1/2″) 18 1.41 0.056
3/8″ BSP (10mm) 15.9mm (5/8″) 19 1.34 0.053
3/8″ NPT (10mm) 15.9mm (5/8″) 18 1.41 0.056
1/2″ BSP (13mm) 20.7mm (13/16″) 14 1.81 0.071
1/2″ NPT (13mm) 20.7mm (13/16″) 14 1.81 0.071
3/4″ BSP (20mm) 26.2mm (1-1/32″) 14 1.81 0.071
3/4″ NPT (20mm) 26.2mm (1-1/32″) 14 1.81 0.071
1″ BSP (25mm) 31.8mm (1-1/4″) 11 2.31 0.091
1″ NPT (25mm) 31.8mm (1-1/4″) 11-1/2 2.21 0.087
1-1/4″ BSP (32mm) 41.3mm (1-5/8″) 11 2.31 0.091
1-1/4″ NPT (32mm) 41.3mm (1-5/8″) 11-1/2 2.21 0.087
1-1/2″ BSP (38mm) 47.6mm (1-7/8″) 11 2.31 0.091
1-1/2″ NPT (38mm) 47.6mm (1-7/8″) 11-1/2 2.21 0.087
2″ BSP (50mm) 58.7mm (2-5/16″) 11 2.31 0.091
2″ NPT (50mm) 58.7mm (2-5/16″) 11-1/2 2.21 0.087
2-1/2″ BSP (65mm) 73mm (2-7/8″) 11 2.31 0.091
2-1/2″ NPT (65mm) 73mm (2-7/8″) 8 3.18 0.125
3″ BSP (80mm) 88mm (3-15/32″) 11 2.31 0.091
3″ NPT (80mm) 88mm (3-15/32″) 8 3.18 0.125
4″ BSP (100mm) 113mm (4-15/32″) 11 2.31 0.091
4″ NPT (100mm) 113mm (4-15/32″) 8 3.18 0.125
6″ BSP (150mm) 163mm (6-15/32″) 11 2.31 0.091
6″ NPT (150mm) 163mm (6-15/32″) 8 3.18 0.125

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