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SI Prefixes

 Note: E (exponent) followed by  + or -   and two digits indicate the power of 10. For example 3.523 907 E-02 = 3.523 907 x 10 to the power of -2  = 0.035 239 07.
Multiplication factors    Prefix SI symbol
1 000 000 000 000 000 000 = E+18 exa E
1 000 000 000 000 000 = E+15 peta P
1 000 000 000 000 = E+12 tera T
1 000 000 000 = E+09 giga G
1 000 000 = E+06 mega M
1 000 = E+03 kilo k
100 = E+02 hecto* h
10 = E+01 deka* da
0.1 = E-01 deci* d
0.01 = E-02 centi* c
0.001 = E-03 milli m
0.000 001 = E-06 micro see **
0.000 000 001 = E-09 nano n
0.000 000 000 001 = E-12 pico p
0.000 000 000 000 001 = E-15 femto f
0.000 000 000 000 000 001 = E-18 atto a
  * To be avoided where practical.    ** Symbol is mu, the 12th letter of the Greek alphabet.
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SI units
Quantity Unit Symbol Equivalent
Base units
Length metre m --
Mass kilogramme kg --
Time second s --
Electric current ampere A --
Temperature kelvin K --
Luminous intensity candela cd --
                
Supplementary units
Plane angle radian rad --
Solid angle steradian sr --
             
Derived units
Frequency hertz Hz s  to power of -1
Force newton N kg m/s2
Work, energy, quantity of heat joule J Nm
Power watt W J/s
Electric charge coulomb C As
Electric potential, electromotive force volt V W/A
Electric capacitance farad F C/V
Electric resistance ohm omega symbol V/A
Magnetic flux weber Wb Vs
Magnetic flux density tesla T Wb/m2
Inductance henry H Wb/A
Luminous flux lumen lm cd sr
Illumination lux lx lm/m2
            
           

Gauges for wire and sheet metal. The sizes given refer to the thickness of sheet or the diameter of wire.

Standard wire gauge. The following gauge numbers correspond to the sizes given in inches;  equivalent sizes in mm are also given to 2 or 3 significant figures.

SWG inch mm SWG inch mm SWG inch mm SWG inch mm
7/10 0.500 12.7 9 0.144 3.66 24 0.022 0.559 39 0.0052 0.132
6/0 0.464 11.8 10 0.128 3.25 25 0.020 0.508 40 0.0048 0.122
5/0 0.432 11.0 11 0.116 2.95 26 0.018 0.457 41 0.0044 0.112
4/0 0.400 10.2 12 0.104 2.64 27 0.0164 0.417 42 0.0040 0.102
3/0 0.372 9.45 13 0.092 2.34 28 0.0148 0.376 43 0.0036 0.091
00 0.348 8.84 14 0.080 2.03 29 0.0136 0.345 44 0.0032 0.081
0 0.324 8.23 15 0.072 1.83 30 0.0124 0.315 45 0.0028 0.071
1 0.300 7.62 16 0.064 1.63 31 0.0116 0.295 46 0.0024 0.061
2 0.276 7.01 17 0.056 1.42 32 0.0108 0.274 47 0.0020 0.051
3 0.252 6.40 18 0.048 1.22 33 0.0100 0.254 48 0.0016 0.041
4 0.232 5.89 19 0.040 1.02 34 0.0092 0.234 49 0.0012 0.030
5 0.212 5.38 20 0.036 0.914 35 0.0084 0.213 50 0.0010 0.025
6 0.192 4.88 21 0.032 0.813 36 0.0076 0.193      
7 0.176 4.47 22 0.028 0.711 37 0.0068 0.173      
8 0.160 4.06 23 0.024 0.610 38 0.0060 0.152      
    

Standard screw threads

In the following, the diameter given is the nominal diameter which is the basic value of the major diameter (over the crests of an external thread).
I.S.O. metric

The table below gives only the first-choice threads in the coarse and fine series. (The constant-pitch series includes threads up to 300mm diameter with pitches of 0.35, 0.5, 0.75, 1, 1.25, 1.5, 2, 3, 4 and 6mm.) The dimensions are in mm. The theoretical thread depths are approximately 0.613 and 0.541 of the pitch for external and internal threads respectively.

Dia.

 Coarse pitch Fine pitch Dia. Coarse pitch Fine pitch
1.6 0.35 -- 16 2 1.5
2 0.4 -- 20 2.5 1.5
2.5 0.45 0.35* 24 3 2
3 0.5 0.35* 30 3.5 2
4 0.7 0.5* 36 4 3
5 0.8 0.5* 42 4.5 3
6 1 0.75* 48 5 3
8 1.25 1 56 5.5 4
10 1.5 1.25 64 6 4
12 1.75 1.25

*These threads form part of the constant-pitch series.

Threads of diameter greater than 70mm in the coarse and fine series are taken from the constant-pitch series, with pitches of 6mm (coarse) or 4mm (fine) and first-choice diameters 72, 80, 90, 100, 110, 125, 140, 160, 180, 200, 220, 250, and 280mm.

Whitworth

The diameters are in inches; the two series are British Standard Whitworth (BSW) and British Standard Fine (BSF). Sizes which are not recommended are excluded here. The theoretical thread depth is approximately 0.640 of the pitch.
Dia.
Threads

BSW
per in.

BSF
Dia.
Threads

BSW
per in

BSF
3/16 24 2 4-1/2 7
1/4 20 26 2-1/4 4 6
5/16 18 22 2-1/2 4 6
3/8 16 20 2-3/4 3-1/2 6
7/16 14 18 3 3-1/2 5
1/2 12 16 3-1/4 5
9/16 16 3-1/2 3-1/4 4-1/2
5/8 11 14 3-3/4 4-1/2
3/4 10 12 4 3 4-1/2
7/8 9 11 4-1/4 4
1 8 10 4-1/2 2-7/8 4
1-1/8 7 9 5 2-3/4 4
1-1/4 7 9 5-1/2 2-5/8 4
1-1/2 6 8 6 2-1/2 4
1-3/4 5 7

       
Unified

The diameter are in inches. There is also an extra-fine series, and a constant-pitch series with threads up to 6in. diameter and pitches corresponding to 32, 28, 20, 16, 8, 6 and 4 threads per inch. The threads are identical in form to the I.S.O. metric threads.

Dia.

 Coarse pitch Fine pitch Dia. Coarse pitch Fine pitch
1/4 20 28 1-3/8 6 12
5/16 18 24 1-1/2 6 12
3/8 16 24 1-3/4 5
7/16 14 20
1/2 13 20 2 4-1/2
9/16 12 18 2-1/2 4
5/8 11 18 2-3/4 4
3/4 10 16 3 4
7/8 9 14
1 8 12 3-1/4 4
3-1/2 4
1-1/8 7 12 3-3/4 4
1-1/4 7 12 4 4
British Association (B.A.)

The dimensions are in mm. No. 0 B.A. is not recommended and only even numbers are first-choice. The theoretical thread depth is 0.6 of pitch.

No. Dia. Pitch No. Dia. Pitch
0 6.0 1.00 13 1.2 0.25
1 5.3 0.90 14 1.0 0.23
2 4.7 0.81 15 0.90 0.21
3 4.1 0.73 16 0.79 0.19
4 3.6 0.66 17 0.70 0.17
5 32 0.59 18 0.62 0.15
6 2.8 0.53 19 0.54 0.14
7 2.5 0.48 20 0.48 0.12
8 2.2 0.43 21 0.42 0.11
9 1.9 0.39 22 0.37 0.10
10 1.7 0.35 23 0.33 0.09
11 1.5 0.31 24 0.29 0.08
12 1.3 0.28 25 0.25 0.07