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Pipe thread

Is there a fairly accurate way to guage pipe thread size?
Male and female? Also what's 3/4" vs 7/8" taper about?
i.e. What size are the heater hose nipple threads
on a BB water pump?


3/8" pipe on the big block heater nipples. There may be some out there that are 1/2" however.

Pipe size has its closest relationship with the inside diameter of the pipe. Note, I said closest, Once you get familiar with pipe threads, you will be able to tell the size by appearance.

1/8" pipe is .405" OD
1/4" pipe is .540" OD
3/8" pipe is .675" OD
1/2" pipe is .840" OD
3/4" pipe is 1.05" OD

The OD of the pipe for a given size is a constant, but the ID varies depending on the Schedule size of the pipe. Schedule 40 is standard, Schedule 5S and 10S are thinner wall, and Schedule 80S and above is thicker wall pipe. The pipe size is approximately the same as the ID for Schedule 40 pipe, but even then it's not a very accurate guess.

The above information is from the Jorgensen Steel/Aluminum Stock List and Reference Book and are nominal dimensions.


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