Pipe Threading

Common pipe thread types:  
NPT or NPS (national pipe tapered or straight): Most common in North America 
MIP or FIP (male or female iron pipe): Same thread dimensions as NPT 
BSP(T) or BSP(S) (British standard pipe tapered or straight): Most common in Europe 
Compression: A unique threaded fitting that does not mate with other thread types
UNS (National Unified Special): Some compatible with compression fittings

NPT Thread Chart

NPT Nominal Size	Actual OD	Hand Tight Turns	Wrench Turns
1/8	0.405"	4.5	2.5
1/4	0.54"	4	3
3/8	0.675"	4.5	3
1/2	0.84"	4.5	3
3/4	1.05"	4.5	3
1	1.32"	4.5	3.25
1 1/4	1.66"	4.5	3.25

BSP Thread Chart 

BSP Nominal Size	Major Diameter (OD)	Minor Diameter (ID)
1/8	0.38"	0.34
1/4	0.52"	0.45
3/8	0.65"	0.59
1/2	0.83"	0.73
3/4	1.04"	0.95
1	1.30"	1.19
1 1/4	1.65"	1.53

What are the parts of a pipe thread?
The thread dimension refers to the major diameter or outside measurement.  
The pitch is the distance from the peak of one crest to the opposite of another. 
The thread angle is the difference between the threads or the valley between the peaks.