Pool Pump Connection Types: Threaded vs Slip

Threaded fittings in a pump listing

A threaded connection, often labeled NPT on a pump listing, uses tapered pipe threads that seal as the fitting is screwed into the pump's inlet or outlet port. Listing words include "threaded", "NPT", "male thread" and "female thread". These words describe the port itself, not the whole pump, so a title may say "threaded inlet" while staying silent on the outlet.

Threaded ports appear on many inground pumps and on some above ground models. The listing usually states the port size alongside the thread word, such as "1.5-inch threaded". That size is a reading cue for an installer, not a figure this site converts or matches to a pool.

Slip fittings in a pump listing

Slip, sometimes written as "glue" or "socket", describes a smooth-bore connection that is joined with PVC solvent cement. A slip port has no threads; the pipe slides into the socket before the joint is made. In a pump title, "slip" is usually paired with a pipe size, for example "2-inch slip".

The word appears most often on above ground pump and pump-and-filter combos. When a listing says "slip inlet" and "threaded outlet", the pump carries both styles, and each port must be matched to the piping connected to it.

Reading the connection words in a pump title

Connection style is a feature word, not a model number. Model codes identify the product line, while "threaded", "slip", "NPT" and "union" describe the ports. A title may name the pump family first and the connection style second, so read the whole phrase before deciding what the listing states.

Titles also use "fits" and "compatible with" as the seller's words. Those phrases are about the pump matching existing plumbing, so they are useful as shopping hints, not as guarantees of a fit. The maker's installation sheet is the authority on what connects to what.

Some listings sell a pump and a separate union adapter as a kit. The title names the pump's port style, and the kit adds the adapter that changes the connection to match a different pipe style. When the listing splits the pump and the adapter, the stated connection style is the pump's native ports, not the adapter's. The same principle applies to a bundled hose or a set of fittings; the attachment is stated in the title, and the pump's ports remain the reading point.

• Threaded or NPT: the port takes a threaded pipe fitting.
• Slip or glue: the port takes a smooth pipe joined with solvent cement.
• Union: a removable threaded collar for service access.
• Not stated by the seller: some listings omit the connection style entirely.

Matching the connection to your piping

The right connection style is the one that matches the piping already at your equipment pad. If the pad has threaded fittings, a threaded port connects directly. If the pad has pipe stubs meant for slip joints, a slip port is the match. Adapters exist, and they are a shopping question, not a recommendation to switch styles.

When a pump listing includes a union, the pump has a removable collar that eases service access, and the union size is usually stated. The related article on pool pump union size covers how that word reads in a title, and pool pump housing thread size explains the port reading in more detail.

What to check before buying

Before comparing models, check three things in the listing: the port size, the connection style on the inlet and the connection style on the outlet. A pump can mix styles, so a single word in the title is not the whole story. The same attention goes to pump-and-filter combos, where the filter's ports are part of the stated package.

This guide explains listing words only. Plumbing work, including cutting, gluing and threading, is done by following the maker's manual and the installer who sets up the pad. Ask the installer what your piping uses before matching a pump. The site's buying guides, such as the best inground pool pump and best above ground pool pump pages, compare stated details of the current catalogue.

The listing may state the connection size in inches, such as "1.5-inch threaded" or "2-inch slip". That figure tells an installer which pipe diameter the port accepts. This site does not convert that size or match it to a pool volume or flow figure; it simply reads the unit as stated. When two listings differ in port size, the maker's sizing page and the installer decide which port fits the pad's piping.

What to pick for your situation

Questions

What does threaded mean on a pool pump listing?

It means the pump's inlet or outlet port takes a threaded pipe fitting, usually tapered NPT threads that seal as the fitting is screwed in. The listing may state the thread size as a nominal pipe size, but the actual fitting is made by the installer.

What does slip mean on a pool pump listing?

Slip, also written as glue or socket, means the port is a smooth-bore socket that is joined to a pipe with PVC solvent cement rather than threads. The listing often pairs the word with a pipe size.

Can a threaded pump connect to slip piping?

Adapters connect the two styles, but the maker's manual and an installer decide whether an adapter fits the pump and the pad. The listing words state the native style, not the adapters available.

What is a union on a pool pump?

A union is a removable threaded collar that lets the pump be disconnected for service. Listings state the union size as a reading cue for the pad.

Do above ground pumps use slip or threaded connections?

Above ground pump and filter combos often state slip ports, while many inground pumps state threaded ports. Each listing states its own ports, and a pump can mix styles.

Should you choose a pump by its connection style?

Connection style is one shopping question among several. Match the port style to your pad's piping, then compare speed type, horsepower and pool type. The best dual speed pool pump and best variable speed pool pump guides cover those comparisons.