basic dimensions for npt american national taper pipe threads
National pipe thread The taper rate for all NPT threads is 1 inch of diameter in 16 inches of length (3⁄4 inch per foot or 62.5 millimeters per meter) measured by the change of diameter (of the pipe thread) over distance of thread. The angle between the taper and the center axis of the pipe is tan−1(​1⁄32) = 1.7899° = 1° 47′ 24″.
Eustachian tube The Eustachian tube, also known as the auditory tube or pharyngotympanic tube,[1] is a tube that links the nasopharynx to the middle ear. It is a part of the middle ear. In adult humans the Eustachian tube is approximately 35 mm (1.4 in) long and 3 mm (0.12 in) in diameter.[2] It is named after the sixteenth-century anatomist Bartolomeo Eustachi.[3]