Spa Filter End Caps & Cartridge Configuration Guide

Pool & Spa Filter Cartridge End Cap Guide

Filter cartridge end caps come in many different shapes, openings, threads, handles, and molded connection styles. Comparing the end caps on your existing cartridge is one of the fastest ways to narrow down the correct replacement.

This visual guide includes 36 common end-cap configurations used on pool and spa filter cartridges. Use the images below to identify the closest match, then confirm the cartridge dimensions and part-number information before ordering.

End-cap style alone does not identify a filter cartridge. Two cartridges can use the same end-cap configuration while having different diameters, lengths, openings, media area, or applications.

Step 1

Compare Both Ends

Identify the top and bottom end caps separately. One end may be open while the other is closed, threaded, or fitted with a handle.

Step 2

Measure the Cartridge

Record overall length, outside diameter, and opening or thread dimensions before choosing a replacement.

Step 3

Use Part Numbers Too

Manufacturer numbers and cross references can confirm a match that dimensions and end-cap appearance alone cannot.

How to Use This End Cap Guide

Start With the Shape

Look closely at the opening, molded lip, raised ring, handle, slots, threads, or locking features. Small differences can separate otherwise similar cartridges.

Then Check the Connection

If the end cap threads into or slips over a fitting, the connection type and size matter. A male slip fitting, SAE thread, MPT thread, and female thread are not interchangeable simply because they appear similar.

Top and Bottom Can Be Different

Many spa cartridges have a handle or closed cap on one end and an open, threaded, or slip-style connection on the other. Record both ends before using a filter finder or cross-reference chart.

Filter Cartridge End Cap Configurations

Search End Cap Styles

Searches the 36 end-cap styles shown below.

No matching end-cap styles were found. Try a broader term such as “open,” “closed,” “handle,” “thread,” or “slip.”

Open

Open With 12 Concentric Holes

Open With 12 Concentric Slots

Open With Raised Ring

Open With Lip Seal

Open With Beveled Edge

Open With Molded Gasket

Open With Molded O-Ring

Open With Slots

Open With Step

Open With Twist Lock

Semi-Circle Handle

Male Slip Fitting

SAE Thread

Male Thread (MPT)

Bar Handle

Castle

Castle With Cross Ribs

Closed

Closed With 2 in SAE Thread

Closed With Three Step Edge

Closed With Raised Ring

Closed With String Handle

Closed With String Loop

Closed With Y Stand-Offs

Hose Fitting

Injection Molded Cone Adapter

Injection Molded Knob Handle

Male Slip Fitting With Molded O-Ring

Male Slip Fitting With MPT

Molded Cone Handle

V-Groove Semi-Circular Handle

Injection molded 1 1/2 inch SAE thread filter cartridge end cap

Injection Molded 1 1/2 in SAE Thread

2 inch female SAE filter cartridge end cap

2 in Female SAE

3 1/2 inch female thread FPT filter cartridge end cap

3 1/2 in Female Thread (FPT)

Dual Bar Handle

What Else Should You Measure?

Overall Cartridge Dimensions

Overall length
Outside diameter
Inside diameter or opening size
Thread or fitting size where applicable

Identification Information

Manufacturer part number
Replacement or cross-reference numbers
Spa or pool manufacturer and model
Any molded or printed markings on the cartridge

Measure the Filter — Not the Opening in the Spa

When possible, remove the existing cartridge and measure the filter itself. Filter housings and wells can be larger than the cartridge, so measuring the compartment instead of the cartridge can lead to the wrong replacement.

Common End Cap Identification Mistakes

Calling Every Threaded End “Threaded”

Threaded filter connections can differ by thread style, diameter, and gender. Match the actual connection rather than only noting that threads are present.

Ignoring Molded Seals or O-Rings

A molded gasket or O-ring can be an important part of how the cartridge seals in the housing. A plain open end may not substitute correctly.

Matching Only the Handle

Bar handles, string loops, cone handles, and semi-circle handles help identify a cartridge, but the opposite end and overall dimensions still have to match.

Assuming Similar Diameter Means Same Filter

Many cartridges share similar diameters while differing in length, opening size, end-cap design, or application.

A Good Match Uses Several Clues

The most reliable replacement combines end-cap style + dimensions + part-number information + application. If all four agree, the risk of ordering the wrong cartridge drops significantly.

Ready to Identify the Filter?

Once you know the end-cap configuration and measurements, use the Filter Finder to search by dimensions, manufacturer, part number, and cross-reference information.

Use the Filter Finder Need Help Finding the Part?

Related Filter Resources

Filter Finder Search by part number, dimensions, manufacturer, and cross-reference information. Filter Cartridge Cleaning Guide Learn how to rinse, deep clean, inspect, and replace pool and spa filter cartridges. Knowledge Base Browse additional pool and spa filter, maintenance, troubleshooting, and identification guides.

End-cap names are descriptive identification aids. Manufacturers may use different terminology for similar configurations. Always verify the complete cartridge specifications before ordering.