Pool and Spa Filter Cross-Reference Numbers, Explained

Pull a filter cartridge out of almost any hot tub and it turns out to have an identity crisis. The one in my tub is a Pleatco PRB25-IN. It’s also a Unicel C-4326. It’s also a Filbur FC-2375. And if I’d bought the tub new, the box would have said Beachcomber 3005845. Four numbers, one cartridge. Nobody really explains this anywhere, so here’s the whole thing.

Why one cartridge has so many names

A filter cartridge is a commodity. Only a handful of companies actually manufacture them, and nearly everyone else, the tub builders, the pool-equipment brands, the online stores, prints their own part number on the same physical part. So the number in front of you depends on who sold it to you, not on what it is. Once you accept that, the whole system stops being confusing and starts being useful, because it means you almost never have to buy the specific box your equipment maker wants you to.

The three aftermarket brands

Three names cover most of the aftermarket, and each one uses its own prefix system. Learn to recognize the prefixes and you can read a part number like a license plate.

Pleatco (the PRB, PWK, PA numbers)

Pleatco is the largest cartridge manufacturer in North America and, for a lot of tubs, the company that made the original filter before anyone rebadged it. Their part numbers use a prefix that hints at the application: PRB on a lot of spa cartridges, PWK on the Watkins-built tubs like Hot Spring, PA on Hayward pool cartridges, PCC on the Pentair Clean and Clear line, and so on. I count 26 different Pleatco prefixes across the cartridges on this site. Every cartridge here lists its Pleatco number first, because it’s the closest thing the industry has to a common standard.

Unicel (the C- numbers)

Unicel puts a C- in front of most of its cartridges: C-4326, C-4950, C-7471. Learn the C- number for one filter and the rest are easy to look up in a catalog, which is a big reason pool stores tend to stock Unicel. A few of the spa cartridges use a slightly different scheme with CH in the middle, like 6CH-940, but the plain C- series covers most of what you’ll run into. Of the 49 cartridges I track, 46 have a Unicel equivalent.

Filbur (the FC- numbers)

Filbur cartridges carry an FC- prefix and move mostly through the dealer network that supplies independent pool stores. Same cartridge, sometimes a better price, occasionally out of stock when the other two aren’t. Filbur covers 43 of the 49 cartridges here; a handful of the odder sizes come only as Pleatco and Unicel, and one lone cartridge, a legacy Sundance filter, has no aftermarket cross-reference at all.

OEM numbers

Then there’s the original number, the one your tub or pool company used. Jacuzzi 373045. Caldera 73533. Hayward CX870-XRE. Pentair R173214. These are the numbers printed in the owner’s manual and, if you’re lucky, still legible on the cartridge. An OEM number is worth knowing because it’s specific to your equipment, but it’s almost always the most expensive way to buy a filter that a generic brand makes for less. Every cartridge in the index lists its OEM equivalents right next to the aftermarket ones. All 49 have at least one.

Are they actually the same filter?

For the large majority of cartridges, yes. Pleatco, Unicel, and Filbur are selling the same pleated media in the same end caps, built to the same dimensions. The sticker is the difference. There’s a longer conversation to be had about whether a generic truly matches the original equipment, which I get into in the generic versus OEM guide, but for a straight cross-reference among the big three you’re comparing price and recent reviews, not quality.

Where cross-references break down

Numbers and dimensions get you almost all the way there. The exception is end caps. Two cartridges can share a diameter, a length, and even a cross-reference table and still have slightly different tops: an open end versus a molded handle, or a 2-inch thread versus a 2⅛-inch opening. If a listed cross-reference has a different cap than what you pulled out, it may not seat.

There’s also the occasional near-match that isn’t one. Jacuzzi’s later J-400 tubs use a cartridge, the 6540-164, that measures within a fraction of an inch of the standard J-300 filter and is not the same part. When two numbers are that close, it’s worth measuring the old cartridge before you trust the chart.

How to actually use a cross-reference

Start with any number you have, even a partial one. Find it on the matching cartridge page and you’ll see every equivalent laid out: the Pleatco, the Unicel, the Filbur, and the OEM numbers, along with the tubs and pool systems that take it. From there, open the listings that are in stock, compare prices, read the recent reviews, and buy the cheapest cartridge with good ones. That is the entire point of a cross-reference: the same filter, at the price you choose. You can start from a brand you recognize on the Pleatco, Unicel, or Filbur pages.

The naming is a mess because the supply chain is a mess, not because the cartridges are complicated. Once you know that PRB25-IN, C-4326, FC-2375, and Beachcomber 3005845 are all the same piece of pleated plastic, the whole thing gets a lot less intimidating and a good deal cheaper.

Don’t have a number to start from? Here’s how to measure a cartridge and find the right one by size.