Thread Types

Short List

Summary - there is National Hose and National Pipe as the main 2 types of threads. National Pipe can be tapered or straight, while National Hose is not tapered.

• National Hose (NH) = National Standard Thread (NST) = National Hose Thread (NHT). It is often referred to as “fire hose thread”. - [1]
• GHT - garden hose Thread, Garden hose thread (GHT) is also referred to as NH. [2]. Same threads per inch as NPT, but not tapered.
• NPSH - national pipe straight hose - same as NPS [3]. Compatible with NPT [4]. NPSH has the same threads per inch as NPT, but without taper. [5]. Verified here [6].
• NPS - National Pipe Straight, same as NPT, but straight. [7]. NPS is not used for high pressure, while NPT can be, such as hydraulics. Does this mean that NPS and GHT are the same?
• NPSM - National Pipe - Straight Mechanical - closure attained by 30 degree compression fit with a swivel - [8]. Only NPT with chamfer will seal properly with NPSM - other NPT threads may not seal.
• NPT - National Pipe - tapered
• R, G - [9]
• BSPP - British Pipe thread parallel
• BSPT - British Pipe thread tapered
• Bolt thread - fine and course
• Metric bolt - fine and course
• Metric pipe straight
• Metric pipe parallel
• UN - [10]
• SAE - with o-rings

Specifications

• 3/4" NPT is 14 threads per inch. [11]
• GHT has 11.5 TPI [12]

Long List

Probably hundreds exist all together.