Pump Information – Imperial or Metric

Ordering the right whirlpool bath pump – The difference between Imperial & Metric fittings.


Are you looking for a replacement whirlpool bath pump? The first thing you need to do is check to whether your existing pump has imperial or metric fittings. The easiest way of doing this is by measuring the thread size. See the diagrams below showing both imperial and metric thread sizes.

Imperial Whirlpool Pump

The diameter of the thread should measure approx. 2 ¼ inches. The teeth of the thread are fairly course compared to that of the metric pump and, as shown in the diagram on the right, you should count 5 teeth per half inch.

Imperial Whirlpool Bath Pump Diagram

Metric Whirlpool Pump

The diameter of the metric pump is slightly wider than that of the imperial and should measure approx. 2 ½ inches. The teeth are quite smooth and closer together, measuring 7 teeth per half inch.

Metric Whirlpool Bath Pump Diagram

Need to purchase a pump?

If you now know what type of replacement whirlpool bath pump you require & would like to purchase one, click either of the buttons below:

Still unsure about what type of pump you have?

If you are still unsure about which whirlpool pump you require, you can call our technical support line Monday – Friday from 8.30am-5.00pm.

For whirlpool bath spare parts & technical support, give us a call on: 01633 244555 & press 2 for technical.