Pool filter cartridge end-cap types

Diameter and length are not enough when the ends connect differently. Read the top and bottom as separate parts, and compare the entire configuration string shown on a cartridge page.

The labels below are strings that actually appear in the Pool Filter Lab dataset. Quotation marks preserve the source wording.

Open ends

An open end has a center passage. The number before the slash is the opening’s inside diameter. Examples include 2-1/8" / open, 3" / open and 6" / open.

Measure the inside diameter straight across the center. The Unicel replacement method specifies ±1/32 inch for an open-end inside diameter.

An opening must match the housing connection or standpipe it fits over. Do not treat two entries as equivalent merely because both say “open”; compare the recorded inside diameter and the shape around the opening.

Open with molded gasket

The dataset uses strings such as 3" / open w/ molded gasket and 4" / open w/ molded gasket.

This looks like an open end with a sealing element formed into the cap around the opening. Compare the opening size and the gasketed profile. A plain open cap and a molded-gasket cap describe different interfaces in the data.

Open with a step, edge or ring

Some entries add a feature around the opening:

• 2-15/16" / open w/ step
• 2-1/2" / open w/ beveled edge
• 4" / open w/ raised ring
• 3-5/8" / open w/ lip seal

Look at the cap in profile as well as from above. The extra contour can determine how the cartridge seats or seals, so preserve the full string when comparing candidates.

Slotted open ends

The data contains 1-7/8" / open w/ slots, 2-3/8" / open w/ slots, / open w/ slots and 4-3/16" / open w/ 12 concentric slots.

Record the opening size when one is given, then note the slot pattern. A slotted face is not described as a plain open face in the dataset. If a source gives / open w/ slots without an inside diameter, treat that dimension as unknown rather than guessing.

Closed ends

/ closed means the cap does not have a central opening. More specific strings include / closed w/ raised ring, / closed w/ Y stand-offs, / closed w/ string handle and / closed w/ string loop.

Check the complete face and its extensions. A closed cap with a ring, stand-off or handle may occupy space that a flat closed cap does not.

Molded cone, bar and semi-circular handles

Handle strings in the dataset include:

• / molded cone handle
• / semi-circular handle
• / v-groove semi-circular handle
• / bar handle
• / dual bar handle
• / injection molded knob handle

Exclude the handle or other extension from the cartridge length measurement. Still match the handle style because it is part of the end-cap configuration and may affect access or clearance.

Male threads and SAE threads

Threaded strings include / 1-1/2” male thread/MPT, / 2” male thread/MPT, / 3" male thread/MPT, / 1-1/4" SAE thread, / 2" SAE thread and / 2" female SAE thread.

Look for an external male thread, an internal female thread or the catalog’s SAE designation. Match the full thread description. A similar-looking diameter does not establish that thread form, sex or connection style is the same.

Some strings combine construction and connection, including / injection molded 1-1/2" SAE thread. Keep that full wording with the measurement notes.

Slip fittings and molded O-rings

The dataset also uses / male slip fitting w/ MPT, / male slip fitting w/ molded o-ring, / 2” male slip fitting and / 1-1/2" male slip fitting.

Compare the projecting fitting, any visible O-ring and any thread. “Slip fitting” and “male thread/MPT” are different labels, even when the end pieces look close at a glance.

PAD adapters and source shorthand

PAD AD appears as a bottom-cap value for Unicel 6CH-22; its paired top-cap value is Handle. These values came from the Pleatco source row and are retained as catalog shorthand.

Do not expand PAD AD into a more specific connection unless the housing documentation or the physical part confirms it. Source shorthand is a reason to verify the equipment model, not a reason to invent a translation.

A compact recording format

Write the wet cartridge’s ends as two separate lines:

Top: opening or closed face, inside diameter if open, gasket/step/slots, handle
Bottom: opening or closed face, inside diameter if open, thread/slip fitting/adapter

Then compare those notes with the exact top-cap and bottom-cap values on the candidate page. If the strings disagree, pause even when the outer dimensions match.