Before revision: Types BSPP fitting Two types of threads are distinguished: Parallel (straight) threads, British Standard Pipe Parallel thread (BSPP; originally also known as British Standard Pipe Fitting thread/BSPF and British Standard Pipe Mechanical thread/BSPM), which have a constant diameter; denoted by the letter G. Taper threads, British Standard Pipe Taper thread (BSPT), whose diameter increases or decreases along the length of the thread; denoted by the letter R. BSPT pipe threads .
After revision: Types BSPP fitting Two types of threads are distinguished: Parallel (straight) threads, British Standard Pipe Parallel thread (BSPP; originally also known as British Standard Pipe Fitting thread/BSPF and British Standard Pipe Mechanical thread/BSPM), which have a constant diameter; denoted by the letter G Taper threads, British Standard Pipe Taper thread (BSPT), whose diameter increases or decreases along the length of the thread; denoted by the letter R. BSPT pipe threads .