ANSI/ASME B1.20.1 is NPT thread, and BSP contains two standards, ISO 228-1 also called BSP parallel thread, and ISO 7-1 also called BSP taper thread. Most of people are confused with these two types of threads. This blog will tell you what’s the difference between ISO 228-1 and ISO 7-1.
What’s ISO 228-1?
ISO 7-1 is BSPP threads(British Standard Pipe Parallel, Whitworth)
Pitch typically measured in threads per inch (TPI)
The truncated regions of crests and roots are rounded.
Angle: 55° Pitch Angle
Standards: DIN ISO 228-1, JIS B0202, BSPP
ISO parallel threads are equivalent to DIN ISO 228-1, BSPP, and JIS B0202. ISO Parallel threads are similar in design to 7/1 threads except there is no taper and there is no interference like the tapered pipe threads of ISO 7/1 or NPT. An O-ring or gasket is normally utilized to seal into the parallel female threaded component. Threads of this type typically provide excellent seal and reseal capability.
What’s ISO 7-1?
ISO 7-1 is BSPT threads(British Standard Pipe Taper, Whitworth)
Thread Taper = 1° 47’
The truncated regions of crests and roots are rounded
Pitch is typically measured in threads per inch (TPI)
Angle: 55° thread angle
Standards: ISO 7-1, BS EN 10226-1, JIS B0203, BS 21, DIN 2999
ISO tapered threads are equivalent to DIN 2999, BSPT, and JIS B0203.
A pipe thread sealant is always required when making up tapered threads.
What’s ANSI/ASME B1.20.1?
ANSI/ASME B1.20.1 is NPT thread(National Pipe Tapered Thread)
Thread taper = 1° 47’
The truncated areas of the roots and crests are flat
Pitch is measured in threads per inch (TPI)
Angle: 60° thread angle
Standards are: ANSI/ASME B1.20.1, SAE AS71051
Some type of pipe thread sealant is always required when making up tapered threads.
The Difference Between Tapered and Paralleled
Tapered Pipe Threads are applied at an angle, typically 1° 47’ to the centerline of the fitting. Tapered threads are designed to seal between the flanks of the threads, but manufacturing tolerances and truncation limits for crests and roots of the fitting do not usually create a leak-tight seal. Tapered pipe threads work by interference fit and will require a sealant to make a leak tight seal. A good sealant is always required to fill the gaps between the roots and crests and to prevent system media from passing through the connection. A good thread sealant will also act as an anti-galling lubricant between the sealing surfaces. Tapered pipe threads, whether they be NPT or ISO, are known as dynamic threads. Sealing is accomplished by thread distortion.
Parallel Pipe Threads (also referenced as straight threads) are applied parallel to the centerline of the fitting. Different from tapered threads which seal on the flanks of the threads, there is no interference between the crests, flanks, and roots of the parallel threads. A gasket (all metal or composite) or O-ring is normally used to seal parallel pipe thread connections. No Teflon tape or sealant is utilized on these threads. There may be, however, certain applications where the installer may wish to utilize a compatible lubricant to reduce galling of these threads. Parallel threads are also known as mechanical threads.
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