Threaded fittings are used extensively to facilitate the connection of components, tubing and hose that make up all pneumatic systems. The different thread types and sizes can be confusing.
Pipe thread and tubing OD are two completely different things. A 1/4” tube fitting doesn't necessarily have a 1/4” threaded connection at the opposite end, you will need to specify both. There are several standard pipe threads including:
NPT is the most commonly used in the U.S. and has a tapered thread. Thread standards should never be mixed on a machine, as a BSPT male thread fitting won’t mate correctly with a NPT female thread fitting (or vise versa). Although they may screw together, the thread angle and shape are different and won’t create a proper seal.
NPT can be referenced multiple ways. MNPT, MPT and NPT(M) all mean the fitting has male threads and uses the NPT standard. Female thread is labeled in a similar fashion, but with an F instead of an M. NPT fittings require thread sealant when installed, such as Teflon tape, but many fittings are provided with sealant already applied from the factory.
NTP threads all have an angle of 60 degrees and the same shape (flat peaks and valleys)
BSPT is sometimes called R-thread or Rc and is most commonly used in Europe, but is also sometimes used in the U.S. and Canada. BSPT fittings require thread sealant when installed, such as Teflon tape, or pre-applied sealant may be supplied on the fitting.
BSPP, also called G-thread or Rp, is less common, and a straight thread, but sometimes needed to connect certain standardized components. BSPP threads don’t require thread sealant since they have an o-ring for sealing.
Both type of BPS threads (BSPT and BSPP) have the same 55 degree thread angle,
with rounded peaks and valleys.
|OD (in)||TPI||OD (in)||TPI||OD (in)||TPI|
Verify fitting sizes using the OD of the pipe and the Threads per Inch (TPI).
(if working with female threads, the ID of the hole will be slightly smaller that the OD values shown)