BSP - British Standard Pipe
Thread Flank Angle - 55º
NOT compatible with NPT thread fittings.
BSP is made in both a tapered (BSPT) and a Parallel (BSPP) version - the air gun industry uses BSPP mostly. BSPP makes an adequate seal by using either an acetal/delrin donut seal inside the female threads or a rubber gasket seal at the base of the fittings (also known as a seal washer or dowty washer). The BSPT creates a seal through its tapered design much like the NPT fittings. Both versions of fittings are known as exotic fittings and are therefore more expensive then NPT.
NPT - National Pipe Tapered
Thread Flank Angle - 60º
Most commonly used in North America, the NPT is made effective because of it's tapered male and female thread thereby forgoing the need for a gasket, although thread sealant is generally used to ensure a proper seal. Though they are similar in look, the NPT and BSP fittings are generally NOT compatible and will not make an adequate seal for pressurized systems.
JIC - Joint Industry Council
Flare - 37º
The JIC fitting is a fitting typified by its 37º flare. The fittings is widely used in fuel delivery and fluid power applications. These fittings are especially good where extremely high pressure is involved. This flare gives the fitting an exceptionally reliable metal-to-metal seal because of the female swivel.
DIN - Deutsches Institut für Normung
DIN fittings are the standard fittings predominately used in SCUBA and SCBA applications. The DIN fitting is a hand tight fitting that seals with an o-ring built into the base of the male side. The threads on a 300 bar DIN corresponds to a CGA 477 fitting.
CGA - Compressed Gas Association
A CGA fitting is standardized system for the attachment of a compressed gas cylinder to the required regulator and/or transfer line. Examples of CGA fittings would be CGA-580 for Non-flamable, Non-oxidizing gasses such as Nitrogen, Argon, or Helium. CGA-590 is used for compressed air and CGA-326 is used for Nitrous Oxide. There are approximately a dozen commonly used CGA-fittings, with others used for special purposes. These fittings are typically used for welding applications, but can extend to other application such as medical and other gas uses.
The fitting standards are designed to make the gas connections leak tight and also prevent different fittings from being mixed up. For example, flamable gas fittings have a left hand thread fittings. Oxygen and inert gases have right hand thread fittings. Since a left hand thread fittings cannot be threaded onto a right hand fitting, it is impossible to connect the fuel gas to the oxygen and vise versa.