Size	OD	Tpi
1/16	5/16	27
1/8	13/32	27
1/4	35/64	18
3/8	43/64	18
1/2	27/32	14
3/4	1-3/64	14
1	1-5/16	11-1/2
1-1/4	1-21/32	11-1/2
1-1/2	1-29/32	11-1/2
2	2-3/8	11-1/2
2-1/2	2-7/8	8
3	3-1/2	8
3-1/2	4	8
4	4-1/2	8

Garden Hose is 3/4" 11.5 tpi. OD is 1 -1/16"

The nominal thread size is from 1/4 - 1/2" smaller than the outside diameter which is completely different than bolt threads. e.g. a vacuum hose barb on a car which has a 1/8" - 27 NPT thread is almost the same as 7/16 - 20 bolt threads.

Tapered threads both join and seal. The deeper you drive them, the tighter the seal.

For a 1/8" pipe D₂ = 0.325 D₃ = 0.345, t₁ Min. = 0.472
See Drilling dimensions at enyge.com for others.

TERMS:
NPT - American Standard Taper Pipe thread
NPTF - Dryseal American Standard Taper Pipe thread
PTF - Same as NPTF except full thread length has been shortened by one threadon small end of thread.- also designated as PTF-SAE Short
PTF Special Short. Same as PTF Short except one full thread has been shortened from large end of thread
PTF - Special Extra Short Same as PTF Short except two full threads has been shortened from large end of thread
NPSF - Dryseal American Fuel Internal Straight Pipe Thread
NPSI - Dryseal American Intermediate Internal Straight Pipe Thread
NPSM - American Standard Straight Mechanical Pipe Thread
NPSH - Straight Pipe Thread
NGO - National Gas Outlet Thread
NGT - National Gas Taper Thread (see "SGT")
GHT - Garden Hose Thread (3/4")
NST - Fire Hose Coupling
BSPT - British Standard Taper Pipe Thread
SAE-LT - 1/4"-28 Taper Thread

Slip - A PVC fitting without any threads that is intended to be glued.
Reamer - A pipe reamer is tapered like a NPT (1:16) tap so the tapered tap has a tapered hole to thread.

See also:
Pipe Thread Specs at AJFittings.com
Tapered Pipe Threads (drilling dimensions) at enyge.com
Taps at N. American Tool
Fire Hose Threads at Akron Brass