threaded fittings overview
This guide provided an overview on the following thread topics
- Taper vs Parallel Threads
- BSP vs NPT Thread Styles
- Metal to Plastic Transition Options
- Install Overview Video
taper vs parallel thread
A tapered thread becomes smaller in diameter the further you travel down the part, whereas a parallel thread maintains a consistent diameter all the way down the part.
When connecting plastic threads to create a pressure-tight seal via wedging, a tapered male into a parallel female or a parallel male into a parallel female is required (shown in diagram).
The plastic fittings supplied by PAAS indicate the thread style using this reference terminology
RP = Parallel female thread, for pressure-tight seal
R = Taper male thread, for pressure-tight seal
G = Parallel female or male thread, where pressure-tight seals are not made on the thread (e.g. barrel unions)
NPT = Tapered male/female
Female – Parallel (w/ring)
Adaptor fittings with a parallel internal pipe thread (RP) and stainless reinforcement ring make it possible to connect plastic and metal pipe.
Important: Metal pipe and fittings should only be threaded into plastic adaptor fittings which have a reinforcement ring.
Male – Taper
Adaptor pipe fittings with a tapered male thread (R) can be bolted into plastic as well as metal sockets.
Female Parallel
FEMALE – PARALLEL
Threaded sockets with tapered internal pipe thread Rp without a reinforcement ring
Threaded fittings (without reinforcement ring) with tapered internal pipe thread Rp allow the establishment of connections between plastic pipe.
NPT VS BSP Thread styles
COMMON QUESTIONS BSP VS NPT
What does BSP & NPT stand for?
NPT is the abbreviation for National Pipe Thread Tapered, which is the U.S. standard for tapered threads used to join pipes and fittings.
(Typically used in America & Canada)
BSP is the abbreviation for British Standard Pipe.
The thread, as defined by the ISO 228 standard, has been adopted as a standard in plumbing and pipe fittings nearly worldwide.
(Typically used in UK, Europe, Asia, Australia and New Zealand)
How do they differ?
Both threads have the same pitch and the familiar shaped peaks and valleys. However, the designs of the threads differ in two fundamental ways. In NPT the peaks and valleys of the threads are flat at an angle of 60 degrees, in BSP the peaks and valleys are rounded with a thread angle of 55 degrees.
But why have two styles, isn’t this just adding confusion?
Yes, but as we in Australia rely on imported products from various global regions these are the standards we’re stuck with.
Typically, BSP threads are the default option we quote and supply, however in some materials (e.g. C-PVC) BSP is not an option because it is produced in America.
Can I join the two styles?
Yes, however only in sizes up to ½”. In sizes above this the pitch thread differs significantly between the two types and will not produce a tight seal.
What are my options when I need to join a BSP thread to a NPT fitting in CPVC?
- Tap a BSP thread into a NPT female thread (we can offer this service up to 1″ only)
- Fabricate an adaptor from solid C-PVC Rod (contact PAAS for more info on 1300 747 464)
Metal to Plastic Threads
Metal Male x Plastic Female
Connect a metal male-thread to a reinforced plastic thread for the best support
Plastic x Metal Adaptors
In some materials such as polyethylene, a plastic x metal adaptor is available
HOW TO CONNECT A MALE PARALLEL FITTING (E.G. IFM ADAPTOR)
In this situation a tap can be run through the female parallel fitting, creating a taper and allowing a seal-tight connection. Contact PAAS for more information on sizing and options.
