THREAD FINDER
  threads per inch  
diameter of bolt in inches   8 9 10 11 12 13 14 16 18 19 20 22 24 26 28 32 36 40 
1/8                                   BSW
3/16                         BSW     BSC
BSF
ME
   
                               
                               
1/4                 NPS
NPT
BSP UNC
BSW
    BSC
BSB
BSF
CEI
UNF UNEF
ME
   
                       
                       
                       
5/16     ACME           UNC
BSW
    BSF UNF BSC
BSB
CEI
  UNEF
ME
   
                       
                       
3/8     ACME         UNC
BSW
NPS
NPT
BSPP BSF   UNF BSC
BSB
CEI
  UNEF
ME
   
             
   
                   
7/16     ACME       UNC
BSW
  BSF   UNF     BSC
BSB
 CEI
UNEF ME    
                     
                     
1/2     ACME   BSW UNC NPT
NPS
BSP
BSF     UNF     BSC
BSB
CEI
UNEF ME    
                 
                 
9/16         UNC
BSW
    BSF UNF   BSC   UNEF BSC
BSB
CEI
       
                       
                       
5/8       UNC
BSW
    BSPP
BSF
UNF         UNEF BSC
BSB
CEI
       
                         
                         
11/16 BSW BSF
3/4     UNC
BSW
  BSF   NPT
NPS
UNF     UNEF     BSC
BSB
CEI
       
13/16     BSW   BSF     CEI
BSB
    UNEF
CEI
BSB
  CEI
BSB
CEI
BSB
       
7/8   UNC
BSW
  BSF     BSPP
UNF
      UNEF     CEI        
15/16   BSW   BSF             UNEF              
1" UNC
BSW
  BSF   UNF   BSPP       UNEF     CEI        
    8 9 10 11 12 13 14 16 18 19 20 22 24 26 28 32 36 40
                                     
BSPP British Standard Pipe Parallel UNC Unified National Course  
BSW British Standard Whitworth UNF Unified National Fine  
BSF British Standard Fine UNEF Unified National Extra Fine  
BSB British Standard Brass ACME from the original manufactor Acme Machinery Co.  
BSC British Standard Cycle NPS American National Straight Pipe  
CEI Cycle Engineers Institute NPT American National Pipe Taper  
ME Model Engineers  

Supplied by DA7C member Peter Marsh with many thanks.  CLICK HERE FOR PRINTABLE PDF VERSION

    BSP

BSP (British Pipe Thread) can be both parallel and tapered. Properly, but never seen, they should be named BSPP and BSPT.  Although the thread form follows the British Standard Whitworth standard, sizes are not the same diameter or number of TPI.  The sizes seem a bit small but were originally based on the inner diameter (measured in inches) of a steel tube for which the thread was intended, but contemporary pipes tend to use thinner walls to save material, and thus have an inner diameter larger than this nominal size.   

The thread for the oil pipe connecting the crankcase to the oil pressure gauge is 1/8" BSP at both ends.

BSP size

Thread
pitch

Major
diam

Minor
diam

Tapping drill

P 95%

T 80%

(in)

(in−1)

(mm)

(in)

(mm)

(in)

(mm)

(mm)

116

28

0.907

0.3041

7.723

0.2583

6.6

6.8

18

28

0.907

0.3830

9.728

0.3372

8.6

8.8

14

19

1.337

0.5180

13.157

0.4506

11.5

11.8

38

19

1.337

0.6560

16.662

0.5886

15.0

15.3

12

14

1.814

0.8250

20.955

0.7335

18.7

19.1

58

14

1.814

0.9020

22.911

0.8105

20.7

21.1

34

14

1.814

1.0410

26.441

0.9495

24.2

24.6

78

14

1.814

1.1890

30.201

1.0975

28.0

28.3

1

11

2.309

1.3090

33.249

1.1926

30.4

30.9