Sheet Metal Thickness Measurement

Many engineering components are produced from a sheet of metal, which is cut to shape and then folded to form the finished article. The edges are then secured by various methods such as welding, brazing, soldering, riveting etc.

The term ‘sheet metal’ is normally used to describe metal sheets with a maximum thickness of 2mm. Above this thickness, it is usual to use the term ‘plate’. The sheets of very low thickness (30 to 50 SWG) are known as foils.

The thickness of metal sheets is identified by a series of numbers, known as Standard Wire Gauge (SWG). Table 1 below lists the SWG numbers and the corresponding thickness or diameter of wire in mm. Table 2 gives the frequently used SWG numbers and their thickness in mm.

Table 1 – SWG Number & Corresponding Sheet Thickness or Wire Diameter

SWG MM SWG MM
7/0 12.700 14 2.032
6/0 11.786 15 1.828
5/0 10.973 16 1.626
4/0 10.160 17 1.422
3/0 9.449 18 1.219
2/0 8.839 19 1.016
8.230 20 0.914
1 7.620 21 0.813
2 7.010 22 0.711
3 6.401 23 0.610
4 5.893 24 0.559
5 5.358 25 0.508
6 4.877 26 0.457
7 4.470 27 0.4166
8 4.064 28 0.3760
9 3.658 30 0.3454
10 3.251 35 0.2134
11 2.946 40 0.1219
12 2.642 45 0.0713
13 2.337 50 0.0254

Table 2 – Most frequently used Standard Wire Gauge

SWG(Number) Thickness in MM (Approx.)
10 3.2
12 2.6
14 2.0
16 1.6
18 1.2
19 1.0
20 0.9
22 0.7
24 0.6

It may be noted that:

(a) Maximum SWG number is 7/0 = 12.70 mm and minimum SWG number is 50 = 0.0254 mm

Also Read  Structure of Materials

(b) 1 SWG = 7.620 mm

(c) Higher the SWG number of a sheet, the lesser will be its thickness.

(d) Lower the SWG number, higher the thickness of the sheet.

Standard Wire Gauge (SWG)

The thickness of the sheet is measured with the help of a standard wire gauge shown in image below. The sheet is put in a suitable slot and SWG number is noted. It is then put in one slot below this test slot and one slot above this test slot. If the grips in these two slots are very tight and loose respectively, then the SWG of test slot is the correct thickness of the sheet.

Although Indian Standard prepared by Bureau of Indian Standards (BIS) formerly ISI (Indian Standard Institute) states that the thickness of sheet and wire should be stated in mm but the practice in industry is still to state the SWG number.

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