Whats the different between M24, 15mm and 20mm tap sizes?

[MrConfused]

How come M24 and 15mm are the same size ? I thought M24 also suppose to mean 24mm

If that means 24mm how come M24 smaller than 20mm .

Cheers

20mmM24

15mm

[EricL]

Hello @MrConfused

Welcome to the Bunnings Workshop community. It's fantastic to have you join us, and thank you for sharing your question about tap sizes.

I can understand how easily you can get confused with the number of plumbing fittings available. Let me try and walk you through the designations to make it easier for you.

Below are the common conventions for tap sizes:

• M24 is a generic reference to a male thread type used in garden and plumbing fittings. The M24 thread type can be used in 15mm or 20mm fittings. Hence when you see M24 part of the fitting is using the fine thread system.
   
• M22 is a generic reference to a female thread type used in garden and plumbing fittings. The most common use is in aerator adaptors from the Kinetic Adaptor Aerator Kit the centrepiece uses an M22 fitting in order to fit into the aerator location.
   
• 15mm BSP (British Standard Pipe) is the common size used in Australia and Commonwealth countries. You'll notice that the threads on these fittings are often tall and farther apart than an M24 or M22 fitting.
   
• 20mm BSP is one of the most common garden fittings used at the moment. However, you'll notice that some older properties used larger garden taps and used 25mm fittings. Some even went as far as using 32mm fittings but those are not commonly used now.

So the plastic garden hose adaptor that you were referring to as the Pope Universal Sprinkler Adaptor earlier in your first picture is actually composed of two parts. One is the main adaptor that is attached to your garden tap and the other part is the one that is attached to your garden hose fitting. In between is a 6mm BSP thread adaptor for a sprinkler system. 

The next picture is the Pope Indoor Tap Adaptor which is used to attach your garden hose to a regular sink or laundry tap with an aerator. This adapter uses an M22 and M24 fitting.

To make it easier when choosing garden fittings, if you have the old fitting, I suggest bringing it with you to the shop to make sure that it is the same size. If you need a particular plumbing fitting, I recommend investing in a Craftright 150mm Digital Caliper. This will guarantee that you'll be getting the correct size all the time.

If you have any other questions we can help with, please let us know.

Eric