You don’t need the faucet’s brand name to identify its cartridge. The physical shape in your hand tells you everything: look at the ears, the retainer style, and whether the stem has splines or a flat locating notch. Match those three features against the descriptions below and you’ll know the family even if the faucet is unmarked, aftermarket, or the handle broke off years ago.
Pull the Stem: What to Check First
Before you can identify anything, get the old cartridge or stem fully out and clean. Here’s the order of operations if you’re mid-teardown and need a checkpoint:
- Shut off water at the stops, then open the faucet to relieve pressure.
- Pop or unscrew the decorative cap on the handle, remove the handle screw, and pull the handle straight off.
- Remove any escutcheon or sleeve covering the valve body.
- Note how the cartridge is held in: clip, screw collar, or threaded bonnet nut. Don’t lose this part.
- Pull the cartridge or stem straight out. If it’s seized, work it with gentle side-to-side rocking, not prying.
Once it’s out, rinse off mineral buildup so you can actually see the ears, splines, and notches. This takes 10 to 15 minutes if nothing is corroded in place, longer if you’re fighting a stuck stem.
Compression vs Cartridge vs Ceramic Disc
These are the three mechanisms you’ll find inside a residential faucet, and the part in your hand will immediately tell you which one you have.
- Compression stem: A threaded rod with a rubber washer screwed to the bottom end. It stops flow by compressing that washer against a seat. If you see a separate rubber washer held on by a brass screw, you have a compression stem, not a cartridge. These need a new seat washer and often a new seat washer screw, not a cartridge replacement.
- Cartridge: A molded plastic or brass sleeve with internal ports that rotates or slides to control flow and mix hot/cold. No separate washer. This is the Moen 1225 and Delta RP family of parts.
- Ceramic disc cartridge: A sealed unit with two flat ceramic discs inside, visible as a wider puck-shaped cartridge with a built-in inlet/outlet pattern on the bottom face. No washer, no spring, nothing to disassemble. This is what you’ll find in Kohler GP-style single-handle faucets and in most modern shower valves and trim that use a mixing cartridge behind the trim plate.
If you’re still not sure, check for a washer first. Compression stems need a seat washer to seal; cartridge and disc designs don’t use one at all. That single detail rules out half the possibilities immediately.
Moen 1225-Style: Visual Identifiers
The Moen 1225 and its direct copies (1200, 1255, 1203) share a distinct shape. Here’s what to look for:
- Two flat, protruding “ears” near the top of the cartridge, roughly opposite each other. These sit in slots in the faucet body and stop the cartridge from spinning.
- A separate U-shaped metal retainer clip that slides in from the side of the faucet body, in front of the cartridge, after the cartridge is seated. This clip is not attached to the cartridge itself. If you pulled a loose metal clip out before you pulled the cartridge, you’re almost certainly looking at a 1225-style setup.
- A stem that’s roughly cylindrical with a flat on one side for the handle adapter, no fine splines running around it.
If your cartridge has ears but no separate clip, and instead a knurled plastic retainer nut screws down over it, you may be looking at a lookalike or a different Moen variant. Ears plus a loose clip is the real tell.
Delta RP-Style: Visual Identifiers
Delta’s RP-series cartridges (RP19804, RP32104, and similar) look superficially similar to Moen’s but the retention method is different and that’s the fastest way to tell them apart:
- No loose clip. Instead, a screw-in retainer collar or dome nut threads directly onto the faucet body and traps the cartridge underneath. You’ll unscrew this collar with pliers or a wrench before the cartridge comes free.
- The cartridge body is usually brass or light gray plastic with a raised tab or pin on top that indexes into the handle adapter.
- Many Delta cartridges have a small plastic retainer clip too, but it’s a thin flat piece that holds the cartridge at the base, not the wide U-clip Moen uses up top. If in doubt, check whether a threaded collar had to come off to free the cartridge. That step is the Delta signature.
Delta also makes a separate line of ball-type single-handle faucets that use a rotating brass or plastic ball instead of a cartridge at all. If you’ve got a dome-shaped cap over a rotating ball with a slot, that’s the older Delta ball valve, not an RP cartridge, and parts for it are different (seats, springs, and the ball itself).
Kohler GP-Style: Visual Identifiers
Kohler’s GP-series ceramic disc cartridges (GP500520, GP77760, and similar) are easiest to misidentify because they don’t look like a “stem” at all. Check for these features:
- A short, wide, puck-like cartridge with two ceramic discs visible on the underside, each with machined openings.
- No splines and no ears on the sides. Instead, there’s a single locating notch or flat edge on the perimeter that lines up with a matching key in the faucet body. This notch is the only thing preventing the cartridge from rotating; there’s no spline engagement with the handle stem itself.
- The handle attaches to a separate stem or adapter that sits on top of the cartridge and engages a raised lug or D-shaped post, not fine teeth.
Because the disc stack does the mixing and sealing, there’s no washer, spring, or seat to replace. If your “stem” looks more like a hockey puck with a notch than a rod with ears, you’re dealing with a ceramic disc design, and Kohler’s GP line is the most common version of it.
Quick Comparison Table
| Feature | Moen 1225-style | Delta RP-style | Kohler GP-style |
|---|---|---|---|
| Retention | Loose U-clip, inserted separately | Screw-in collar or dome nut | Notch/key, no separate retainer |
| Stem features | Two flat ears, no splines | Raised tab, sometimes fine splines | No ears or splines, single locating notch |
| Washer present | No | No | No |
| Shape | Narrow cylindrical | Narrow cylindrical | Wide, flat puck |
Confirm Match Before Ordering Parts
Don’t rely on memory once you’ve set the old cartridge down. Take two photos before you buy anything: one straight-on showing the ears or notch pattern, and one from the side showing the retainer style (clip, collar, or none). Measure the overall length and diameter with calipers or a tape measure, since lookalike cartridges from different manufacturers can be close enough to confuse but off by a few millimeters, which is enough to leak or bind.
If the retainer clip or collar is missing, corroded beyond reuse, or you’re not sure it’s original to the faucet, replace it along with the cartridge. Mismatched retainers are a common cause of handles that feel loose or faucets that drip right after a repair. If you’ve matched all three features above (ears or notch, retainer style, and presence or absence of a washer) and you’re still getting two conflicting matches, pull the faucet body’s model stamp if one exists, usually on the underside or back of the valve body, and cross-reference that against the cartridge shape rather than guessing from the handle design alone.