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
Table 2 – Most frequently used Standard Wire Gauge
|SWG(Number)||Thickness in MM (Approx.)|
It may be noted that:
(a) Maximum SWG number is 7/0 = 12.70 mm and minimum SWG number is 50 = 0.0254 mm
(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.