For a hidden aerator, get a key set that covers all four Caché sizes, like the Neoperl 1191705, which includes Standard, Junior, Tiny Junior and Tom Thumb keys. If your faucet maker sells an aerator with its own wrench for your model, such as Delta’s RP54977 for listed Delta faucets, that is the exact match.
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This guide covers keys for removing and installing hidden faucet aerators.
Aerator keys compared
| Key | Fits | Choose it when |
|---|---|---|
| Neoperl 1191705 key set | Caché sizes Regular (STD), Junior, Tiny Junior and Tom Thumb | You do not know which hidden aerator size you have |
| Delta RP54977 | A replacement aerator with its own plastic wrench for listed Delta faucets | Your Delta faucet model is on the listing |
Many modern faucets hide the aerator inside the spout, so there is no outer ring to grip. You can only see a small round insert, and the only way to unscrew it is with a key that locks into its face. Without the right key, people end up gouging the spout with pliers.
How to tell if you have a hidden aerator
Look at the end of the spout. A standard aerator has a metal or plastic ring with flats or a knurled edge that sticks out and can be turned by hand or with a cloth and pliers. A hidden aerator sits flush or recessed inside the spout with no outside threads showing.
Neoperl, which makes the widely used Caché hidden aerator, says on its blog (neoperl.com) that you can recognize a Caché aerator by its blue rubber seal, that it only fits a faucet with a special bore, and that it can only be replaced by a Caché aerator of the same size.
Our faucet aerator guide covers standard male and female aerators and how to measure them.
Hidden aerator sizes
Neoperl’s Caché product page (neoperl.com) lists four sizes: M24x1 (Standard, STD), M21.5×1 (Junior, JR), M18.5×1 (Tiny Junior, TJ) and M16.5×1 (Tom Thumb, TT). Each size takes its own key, which is why most kits include several.
Neoperl also lists Caché models by flow rate, stream type and features such as an adjustable stream angle, automatic cleaning and an easy-clean elastomer surface, and notes that the range is for the normal pressure range of 20 to 80 psi. When you replace one, match both the size and the flow rate printed on the old insert or in the faucet maker’s parts list.
Flow rate matters because the aerator sets how much water the faucet delivers. Neoperl lists Caché inserts in several flow categories, from about 1.0 gpm up to higher-flow versions, plus pressure-compensating models. Putting a higher-flow insert in a bathroom faucet can change how it performs, so replace like with like unless the faucet maker lists an alternative.
If you cannot read the size on the old insert, measure the opening against the four sizes above, or bring the old aerator to the store. The thread size is the first number: 24, 21.5, 18.5 or 16.5 millimeters.
Neoperl 1191705: the four-key set
Choose the Neoperl 1191705 if you are not sure which size you have. Ferguson’s listing (ferguson.com) of the Neoperl part describes four color-coded keys for Regular, Junior, Tiny Junior and Tom Thumb Caché aerators. The Amazon listing gives the matching thread sizes, M24, M21.5, M18.5 and M16.5 x 1, and warns that the keys fit Caché-style aerators only, not slim aerators.
Try the keys from largest to smallest until one seats fully in the insert, then turn counterclockwise.
On October 15, 2026, the standard new offer from a third-party seller showed stock under the title Neoperl 1191705.
Check Neoperl 1191705 Caché aerator key set on Amazon →
Delta RP54977: an aerator that comes with its wrench
Choose the Delta RP54977 only if your Delta faucet is on its list. The listing describes a 1.5 gpm aerator with a plastic wrench, 13/16-27 male threads, made for Delta faucets 1353-DST, 3353-DST, 4453-DST and 11926-DST. Some faucet makers sell replacement aerators packed with a matching key like this, so check your faucet’s parts list before buying a universal kit.
On October 15, 2026, the standard new offer sold by Amazon.com showed stock with part RP54977.
Check Delta RP54977 aerator with wrench on Amazon →
When the aerator is stuck
Mineral scale often locks a hidden aerator in place. Neoperl’s stuck aerator guide (neoperl.com) suggests soaking the aerator in a limescale remover held on with a small bag and tape, or spraying it with WD-40 and waiting about five minutes, then turning it counterclockwise with the right service key.
As a last resort, Neoperl describes driving two small screws into opposite sides of the aerator’s strainer and using them to turn it out, and warns the aerator cannot be reused after that. Go carefully so you do not damage the spout threads.
Our aerator cleaning guide covers soaking and cleaning once it is out.
Putting the aerator back
Clean any grit out of the spout threads, check the rubber seal and replace it if it is flattened or torn, then thread the aerator in by hand with the key until it is snug. Do not overtighten a plastic aerator; snug is enough to seal.
Before reinstalling, flush the spout: with the aerator out, run the water for a few seconds to clear any loose scale or debris from the line, especially after plumbing work upstream. Debris left in the spout is what clogs a new aerator within days. Hold a cup under the spout so loose grit does not go down the drain and into the trap.
Run the water and check for spray around the edge. If it leaks, the seal may be missing or the aerator may be cross-threaded; back it out and start again.
Why a key beats pliers
Pliers and wrenches only grip the outside of the spout, which on a hidden aerator is the faucet itself, not the aerator. That scratches the finish and can bend a thin spout without moving the aerator at all. A key engages the aerator directly, so the force goes where it is needed.
The key matters most on kitchen pull-down and pull-out sprayers and on modern bathroom faucets, where the aerator is often recessed. A sprayer head with a molded face may have no removable aerator at all; check the faucet maker’s parts list before you go looking for a key.
Keep the key under the sink or tape it inside a cabinet door so it is there the next time the stream starts to spray sideways.
Frequently asked questions
What is an aerator key?
A small tool that locks into the face of a hidden aerator so you can unscrew it from inside the faucet spout.
What sizes do hidden aerators come in?
Neoperl lists Caché sizes M24x1 (Standard), M21.5×1 (Junior), M18.5×1 (Tiny Junior) and M16.5×1 (Tom Thumb).
How do I know if my aerator is a Caché?
Neoperl says you can recognize a Caché aerator by its blue rubber seal inside the spout.
How do I remove a stuck hidden aerator?
Neoperl suggests soaking it in limescale remover or WD-40, then turning it with the correct service key.
Can I use pliers on a hidden aerator?
Not effectively. Pliers grip the spout, not the aerator, and can scratch or bend the faucet.
How we chose
This document-based guide makes no hands-on testing claim. We read Neoperl’s Caché aerator page and its guide to removing a stuck Caché aerator, and Ferguson’s listing for the Neoperl 1191705 key set. The Delta aerator is described from its listing. A Danco key was excluded because its Amazon part number did not match the maker page. On October 15, 2026, both linked standard new offers showed stock. Read our selection method and about Plumbing Picks.
Primary sources
- Neoperl Caché faucet aerators (neoperl.com): sizes M24/M21.5/M18.5/M16.5 x1, features, 20–80 psi range.
- Neoperl: Help, my Caché aerator is stuck (neoperl.com): blue seal, same-size replacement, service keys, soak/WD-40/screw methods.
- Ferguson: Neoperl 1191705 key set (ferguson.com): four color-coded keys: Regular, Junior, Tiny Junior, Tom Thumb.