Aerator Thread Sizes Explained

Male, female, and why it is not obvious

An aerator thread is described from the aerator's point of view, not the tap's. A male aerator has the thread on the outside of its shell and screws up inside the spout. A female aerator has the thread inside and screws down over the outside of the spout.

Look at the spout, not the old aerator: if you can see a thread on the outside of the spout, you need a female aerator. If the spout is smooth outside and threaded inside, you need a male one. Getting this wrong is the single most common ordering error in this category.

The sizes that actually matter

M24*1 male and F22*1 female carry most of the range and cover most European spouts. M20*1 appears for American thread sizes. M22*1 shows up on the brass swivel adaptors, which is what you use to step a thread rather than change the whole spout. M28*1 turns up mainly on the service keys, and the hidden basin mixer body uses a 21.5*1 female thread.

The number is the outside diameter in millimetres and the *1 is the pitch — one millimetre between thread crests. A thread gauge settles it in seconds; a photograph rarely does.

Swivels are thread adaptors that also move

The brass swivels in this range come in M24 to M24, M24 to M22 and M22 to M22. Two of those change the thread size, which means a swivel can solve an adaptation problem and a reach problem in the same fitting.

They also do the job people actually buy them for: turning a full 360 degrees so the stream can be aimed into the corners of a sink that a fixed spout will never reach.

Hidden and vandal threads need their key

Hidden and vandal-resistant shells have no flats to grip, which is the point. They come out with a service key and nothing else. The key in this range is specified for M22x1 or regular female, M24x1 or regular male with side flats, and M28x1.

Order the keys at the same time as the aerators and keep them somewhere other than the site toolbox. A tamper-resistant aerator whose key has been lost is a tamper-resistant aerator for your own maintenance team too.

What to send with an enquiry

Three things settle almost any aerator order: whether the spout thread is inside or outside, the diameter in millimetres, and the flow rate your specification or local code requires. With those, the shell and the core can both be chosen.

If the flow rate is the awkward part, say so. On the vandal-resistant and hidden bodies the core is the part that changes — 2L, 4L, 6L, 8L and 9L are documented on one body — while the shell stays the same.