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Reference guide to selecting the size of pipe thread





Male threads: Measure the outside diameter of the large portion of the thread at "A"; Find figure nearest this dimension in column 1 or 2 of chart. The dimension in column 3 will be your nominal pipe thread size.


Female Threads: Measure top diameter of thread at "B"; Find figure nearest this dimension in column 1 or 2 of chart. The dimension in column 3 will be your nominal pipe thread size.




Definition of pipe thread acronyms
NPT National Pipe Thread
FPT Female Pipe Thread
MPT Male Pipe Thread
PTF SAE short tape pipe thread
NPTF American National taper pipe thread for dryseal pressure-tight joints
NPSM American National straight pipe thread for mechanical joints
NPSI American National straight intermediate pipe thread


Two common pipe thread sizes exist, the tapered National Pipe Thread (NPT) and the straight National Standard Free-Fitting Straight Mechanical Pipe Thread (NPSM). The tapered threads are for joining and sealing, the straight threads are only for joining. The Dry-seal thread (NPTF) allows for joining without sealants. Three less common threads exist, the Garden Hose Thread (GHT), Fire Hose Coupling (NST) and British Standard Taper Pipe Thread (BSPT). The NPT and NPTF threads are interchangeable with sealants such as PTFE tape. None of the other thread standards are interchangeable. Female NPT threads can be designated as "FPT" and male NPT threads can be designated as "MPT."

Pipe sizes do not refer to any physical dimensions. The outside diameter of each pipe or fitting must be measured and compared to the table for size identification. For example, a 3/4" NPT pipe thread has an outside diameter of 1.050 inches. Each thread size has a defined number of threads per inch (TPI). The 3/4" NPT pipe thread has 14 threads per inch. Both the TPI and OD of the thread are required for positive identification of thread size because several sizes have the same TPI.
 

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Discussion Starter #7
saber07 said:
uhh, isnt cfm cubic feet per minute as in regards to air compressors?
CFM is a standord way of mesuring flow rate,
as in Cubic Feet of air a Min.
 

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well, im trying to figure out if its really worth it to upgrade line to 3/4 or 1" instead of my 1/2" plastic line

it may not be as easy as it sounds, but im consistantly impressed by stuff you post, so i figured if anyone know, you prolly would
 

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dragginbody365 said:
well, im trying to figure out if its really worth it to upgrade line to 3/4 or 1" instead of my 1/2" plastic line

it may not be as easy as it sounds, but im consistantly impressed by stuff you post, so i figured if anyone know, you prolly would
if anything you will notice a diff in 5/8" line

I am still working on the formula

I will let you know.
 

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You pretty much have to pick a fixed pressure to calculate cfm's between the two because different pressures will push the air through the pipe at different cfm's. Correct me if I'm wrong.
 

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02 s-10 xtreme said:
You pretty much have to pick a fixed pressure to calculate cfm's between the two because different pressures will push the air through the pipe at different cfm's. Correct me if I'm wrong.
you make a good point,

to calcuate the CFM and choked flow artes froma pressurized tank 15PSI+ to a empty vessle 0PSI you need to use this formula,

CD (A / V) (g R / M)1/2 [(k - 1)/(2k)] k3/2 [2/(k + 1)]a (T0 / P0b)1/2 (t2 - t1) = P2c- P1c

:eek:

I will make it into a claculator ;)
 
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