Pool Pump Housing Thread Size: NPT vs BSP
Short answer: Pool pump housing ports are listed with a thread standard and a nominal size, such as NPT or BSP followed by a number in inches. NPT means National Pipe Thread, the tapered standard common on North American equipment. BSP means British Standard Pipe, the standard on pumps made for other regional markets, with parallel or tapered forms. The listing states which one the housing uses, and the number names the nominal pipe size, not the actual thread diameter. Matching the stated standard to your plumbing is a shopping question, and the maker's manual and an installer decide the connection.
What a thread size is in a pump listing
Pool pump titles and spec tables state the ports on the pump housing with two pieces of information: a thread standard and a size figure. The standard is a code such as NPT, BSP, BSPT or BSPP. The size reads as a number, often written in inches. Together these describe the threaded connection on the inlet and outlet ports where the plumbing attaches. The words in a listing tell you which standard the maker built the housing for, which is why two pumps with the same size number may not accept the same fittings.
Thread size is a listing question, not a measured one on this site. The site compares stated details in the title and spec table and does not convert or verify thread measurements. When a seller does not print the standard, the connection type is unstated by the seller, and the reader reads the maker's manual or asks an installer. See how pump connections are listed for the wider set of connection terms.
- NPT: National Pipe Thread, tapered
- BSP: British Standard Pipe, covers both BSPP and BSPT
- BSPP: parallel threads, also written G
- BSPT: tapered threads
NPT as a listing term
NPT stands for National Pipe Thread, a US standard for tapered pipe threads. Tapered means the thread diameter changes slightly along the length of the fitting, so a male NPT fitting wedges into the female port as it turns in. NPT is common on pool equipment made for the North American market, and the code NPT appears in pump titles and spec tables of pumps that state a threaded connection.
When a listing carries NPT with a size number, the number is the nominal pipe size, which is close to but not equal to the actual measured diameter of the thread. The listing states the standard; the connection work is left to the installer following the maker's manual.
BSP as a listing term
BSP stands for British Standard Pipe, a thread standard used on equipment made for markets outside North America, including the UK, Australia and parts of Europe and Asia. Inside BSP there are two forms. BSPP names parallel threads, where the diameter stays the same along the fitting, and BSPT names tapered threads that wedge like NPT.
A pool pump listing that carries BSP tells you the housing was made for the BSP standard, and NPT fittings are not a direct match. BSP and NPT sizes are not interchangeable even when the nominal number reads the same.
Tapered versus parallel threads
The two standards differ in geometry. Tapered threads, which include NPT and BSPT, get slightly narrower toward the end of the fitting, so the seal forms where the metal wedges together. Parallel threads, which include BSPP, keep the same diameter along the fitting and rely on a washer or O-ring at the face of the joint.
In a listing, the standard code shows which geometry the housing uses. A reader comparing two pump listings with the same size number but different standards is not comparing two compatible housings; the words NPT and BSPP mean different connection geometry.
| Standard | Geometry | Regional use |
|---|---|---|
| NPT | Tapered | North American equipment |
| BSPP | Parallel | UK, Australia, parts of Europe and Asia |
| BSPT | Tapered | UK, Australia, parts of Europe and Asia |
How the size number reads
The size number in a pump listing names the nominal pipe size, not the outside diameter of the fitting or the thread count. A listing that states a number followed by NPT names the nominal size of the line the port is built for, and the actual thread outside diameter on the fitting measures differently from that number. The same convention holds for BSP: the listing number is nominal, and the thread pitch is part of the standard, not an extra specification the seller prints.
For shopping, what matters is that the number and the standard appear together in the listing. A title that shows a number without the standard leaves the connection type unstated by the seller, and the reader reads the spec table or the maker's manual to find which standard the housing uses. Related articles on this site cover union sizes and piping size recommendations in listing terms.
Threads and regional markets
Which standard a pump carries often tracks the market the listing is aimed at. NPT is common on pumps made for North American distribution, while BSP appears on pumps built for export or for brands that sell in several regions. This is a listing clue, not a rule stated by the makers.
A pump sold on the same catalog page may carry NPT in one model and BSP in another, so the regional hint does not replace reading the standard in the title or spec table. The best guide is the maker's manual and the stated spec on the pump page.
What to check when shopping
Three questions come up when a pump listing states a thread size. First, what does your existing plumbing use, NPT or BSP? Second, does the listing state the standard on the housing, or is the connection type left as not stated by the seller? Third, does the pump model come with unions or adapters, or is the port a bare threaded connection?
The answer to the first question comes from looking at your current pump's housing or asking the installer who set up the pad. The second and third are answered by reading the listing's spec table and the maker's manual. This article does not tell you which fittings will connect; that depends on the specific parts and is decided by the installer following the maker's instructions. When you know your standard, compare pumps with the same statement in the inground pump guide or the above ground pump guide.
What to pick for your situation
| If you | Pick | Buying guide |
|---|---|---|
| Your current pump housing and plumbing use NPT threads | A pump whose listing states NPT on the inlet and outlet ports | Best Inground Pool Pumps (2026): 15 Picks |
| Your current pump housing and plumbing use BSP threads | A pump whose listing states BSP on the inlet and outlet ports | Best Above Ground Pool Pumps (2026): 15 Picks |
| You are replacing a pump and the listing shows a size number with no standard | Read the spec table and the maker's manual to find the stated thread standard before comparing models | Best Hayward Pool Pumps (2026): 15 Picks |
| You want a variable speed pump and the thread standard must match your plumbing | A variable speed pump whose listing carries the same thread standard as your existing connections | Best Variable Speed Pool Pumps (2026): 15 Picks |
| You own an above ground pool and the pump ships in a sand filter combo | A combo whose listing states the same thread standard for pump and tank ports | Best Sand Filter Pump for Above Ground Pools (2026) |
Questions
What does NPT mean on a pool pump?
NPT stands for National Pipe Thread, a US standard for tapered pipe threads. The code appears in pump listings to state the thread standard the housing ports are built for.
What does BSP mean on a pool pump?
BSP stands for British Standard Pipe, a thread standard used on equipment made for markets outside North America. BSP includes parallel threads (BSPP) and tapered threads (BSPT).
Can NPT and BSP fittings be used together?
No. NPT and BSP are different thread standards with different geometry and pitch, and fittings for one are not a direct match for the other.
What does the size number mean next to NPT or BSP?
The number names the nominal pipe size in inches, not the actual thread diameter. The thread pitch is part of the standard, not a separate item in the listing.
Where do you find the thread standard for your pump?
The listing title or spec table states it when the seller prints it. If the standard is not stated, read the maker's manual.
Are NPT threads tapered and BSP threads parallel?
NPT threads are always tapered. BSP has both forms: BSPT is tapered and BSPP is parallel, so a BSP listing does not by itself name the geometry.
Recent updates
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