How to Measure BSP Threads and PVC Pipe

Posted by showeradm 21/05/2018 0 Comment(s)

Most sprinklers have a 15mm or 20mm female thread at the inlet of the sprinkler. For most people who aren't familiar with thread sizes, it's easy to assume that measuring the thread with a ruler will indicate the size of the fittings needed. Unfortunately doing this will result in ordering fittings that are not the correct size (usually too big). If you have a fitting or pipe that you need fittings for, manufacturers will usually have the size printed, stickered or embossed on the fitting itself. That's a guaranteed way to know what size fittings you need. If you are unable to find any markings, the information below will help you select the right size fitting or pipe you need!

In Australia the naming convention for thread sizes follows the BSP (British Standard Pipe) standard. There are male (BSPM) and female (BSPF) threads. BSP threads and PVC Pipe have nominal sizes, meaning they are only called '15mm' or '20mm', but do not actually measure to that size. offers a range of fittings range from 15mm to 80mm with BSP thread sizes. Sometimes these fittings may be referred to in imperial form. For threads and PVC Pipe: half inch refers to 15mm, three quarter inch refers to 20mm, one inch refers to 25mm, one and a quarter inch refers to 32mm, one and a half inch refers to 40mm, two inch refers to 50mm.

To find out what size threaded fitting you have, measure the outer diameter of male threads and inner diameter of female fittings.

*image not to scale, measurements are appoximates only.


Similarly PVC pipe and slip fittings have the same measuring method. For PVC Pipe measure the outer diameter, for the fittings measure the inner diameter. If a PVC fitting has a thread, please refer to the BSP chart above.

*image not to scale, measurements are appoximates only.


Lastly, Garden Taps have a slightly different naming convention as well. A standard 15mm garden tap has a 15mm BSP Male threaded inlet and 20mm BSP Male threaded outlet. A 20mm garden tap has a 20mm BSP Male threaded inlet and 25mm BSP Male threaded outlet.


*image not to scale, measurements are appoximates only.


All the above information is based on BSP threads, which is the standard in Australia. There are few fittings floating around in the country that have NPT threads (National Pipe Thread) which is the standard used in the USA. If you happen to have these fittings, you can use them with BSP threads upto 25mm. Any bigger and you will need to find an appropriate NPT to BSP adaptor.


Happy irrigating!

-Aki Iyer