Post by Warwick (Ozcoupe) on Nov 6, 2007 2:25:06 GMT
I just found this well-written history of threads.
All those who are familiar with the subject, please excuse.
www.internationalcockpitclub.org.uk/articles/article_threads.htm
It doesn’t say much about pipe threads.
BSP is the British Standard Pipe thread and comes in 2 types.
BSPT: Tapered thread – used to provide a self-sealing joint between pipes and fittings. Because of the taper (which is visible), the joint gets tighter and tighter as the parts are screwed together until they eventually jam.
BSPP: Parallel thread which will just keep screwing together until you run out of thread.
BSP was adopted into the metric system as the pipe thread but with the size being given in millimetres.
The US standard is NPT (National Pipe Thread) and from ½” size down the difference between BSPT and NPT is slight and can usually be used interchangeably without damage. This is particularly the case for the small sizes 3/8”, ¼” and 1/8”.
Pipe tends to have heavier wall thickness and is joined by cutting a thread on the outside and screwing together, or butt-welding.
Pipe size is determined by the bore of the pipe. A ½” pipe has a ½” hole down the middle.
Pipe fittings sizes are determined by the size of pipe that will screw into them. A ½” pipe elbow has a threaded hole large enough to take a ½” pipe, so the hole is a lot bigger than ½”.
Tube tends to have a thinner wall and is joined by slipping it inside a fitting that squeezes in on it to seal using ferrules or O-rings, etc., or it is brazed or soldered into the fitting. It may also be flared at the end and used in a fitting that squeezes the flared end against a nipple of similar profile.
Tube sizes are determined by outside diameter. A ½” tube will fit neatly into a ½” hole while the hole down the centre of the tube is less than ½” by the thickness of the wall.
Tube fittings sizes are also determined by the size of the tube that they accept and so a ½” tube elbow has a ½” hole.
Hoses are hose pipes and so are measured by the inside diameter or bore. Plastic tubing is tube and is measured by its OD. (Usually!)
This is why a ½” steel water pipe is so much bigger that a ½” copper tube.
Plumbing fittings associated with engines, such as pressure and temperature fittings that screw into the block will generally be BSPT (or NPT across the pond) and so if they are ½” or less they will be interchangeable without damage. (1/2” being the borderline size). But thread tape should be used of course.
Warwick.
All those who are familiar with the subject, please excuse.
www.internationalcockpitclub.org.uk/articles/article_threads.htm
It doesn’t say much about pipe threads.
BSP is the British Standard Pipe thread and comes in 2 types.
BSPT: Tapered thread – used to provide a self-sealing joint between pipes and fittings. Because of the taper (which is visible), the joint gets tighter and tighter as the parts are screwed together until they eventually jam.
BSPP: Parallel thread which will just keep screwing together until you run out of thread.
BSP was adopted into the metric system as the pipe thread but with the size being given in millimetres.
The US standard is NPT (National Pipe Thread) and from ½” size down the difference between BSPT and NPT is slight and can usually be used interchangeably without damage. This is particularly the case for the small sizes 3/8”, ¼” and 1/8”.
Pipe tends to have heavier wall thickness and is joined by cutting a thread on the outside and screwing together, or butt-welding.
Pipe size is determined by the bore of the pipe. A ½” pipe has a ½” hole down the middle.
Pipe fittings sizes are determined by the size of pipe that will screw into them. A ½” pipe elbow has a threaded hole large enough to take a ½” pipe, so the hole is a lot bigger than ½”.
Tube tends to have a thinner wall and is joined by slipping it inside a fitting that squeezes in on it to seal using ferrules or O-rings, etc., or it is brazed or soldered into the fitting. It may also be flared at the end and used in a fitting that squeezes the flared end against a nipple of similar profile.
Tube sizes are determined by outside diameter. A ½” tube will fit neatly into a ½” hole while the hole down the centre of the tube is less than ½” by the thickness of the wall.
Tube fittings sizes are also determined by the size of the tube that they accept and so a ½” tube elbow has a ½” hole.
Hoses are hose pipes and so are measured by the inside diameter or bore. Plastic tubing is tube and is measured by its OD. (Usually!)
This is why a ½” steel water pipe is so much bigger that a ½” copper tube.
Plumbing fittings associated with engines, such as pressure and temperature fittings that screw into the block will generally be BSPT (or NPT across the pond) and so if they are ½” or less they will be interchangeable without damage. (1/2” being the borderline size). But thread tape should be used of course.
Warwick.
