[AWG 15 seems to fit the bill for most devices]
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American Wire Gauge (AWG)

AWG Inches mm      AWG Inches mm
50 0.00100 0.025   29 0.0113 0.287
49 0.00110 0.028   28 0.0126 0.320
48 0.00124 0.031   27 0.0142 0.361
47 0.00140 0.036   26 0.0159 0.404
46 0.00157 0.040   25 0.0179 0.455
45 0.00176 0.045   24 0.0201 0.511
44 0.0020 0.051   23 0.0226 0.574
43 0.0022 0.056   22 0.0253 0.643
42 0.0025 0.064   21 0.0285 0.724
41 0.0028 0.071   20 0.0320 0.813
40 0.0031 0.079   19 0.0359 0.912
39 0.0035 0.089   18 0.0403 1.02
38 0.0040 0.102   17 0.0453 1.15
37 0.0045 0.114   16 0.0508 1.29
36 0.0050 0.127   15 0.0571 1.45
35 0.0056 0.142   14 0.0641 1.63
34 0.0063 0.160   13 0.0720 1.83
33 0.0071 0.180   12 0.0808 2.05
32 0.0080 0.203   11 0.0907 2.30
31 0.0089 0.226   10 0.1019 2.60
30 0.0100 0.254

http://www.coilcraft.com/awg.cfm

STANDARD WIRE GUAGE  
http://www.imetalindia.com/swg.html
 
SWG No. Dia. mm SWG No. Dia. mm SWG No. Dia. mm
7/0 12.7000 13 2.2368 32 0.2743
6/0 11.7856 14 2.0320 33 0.2540
5/0 10.9728 15 1.8288 34 0.2337
4/0 10.1600 16 1.6256 35 0.2134
3/0 9.4488 17 1.4224 36 0.1930
2/0 8.8392 18 1.2192 37 0.1727
1/0 8.2296 19 1.0160 38 0.1524
1 7.6200 20 0.9144 39 0.1321
2 7.0104 21 0.8128 40 0.1219
3 6.4008 22 0.7112 41 0.1118
4 5.8928 23 0.6096 42 0.1016
5 5.3848 24 0.5588 43 0.0914
6 4.8768 25 0.5080 44 0.0813
7 4.4704 26 0.4572 45 0.0711
8 4.0640 27 0.4166 46 0.0610
9 3.6576 28 0.3759 47 0.0580
10 3.2512 29 0.3454 48 0.0406
11 2.9464 30 0.3150 49 0.0305
12 2.6416 31 0.2946 50 0.0254

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