(cylinder capacity) by 7 (one-seventh of the cylinder capacity). As a safety precaution, it is recommended that flashback  arrestors be installed between the regulators and the gas  supply hoses of all welding outfits.  Figure 5-21  shows  recommended tip sizes of different manufacturers, for  welding various thickness of metals.  The working pressure should be set according to the  manufacturer’s recommendation for the tip size that is being  used to weld or cut. This is a recommended method that works  for most welding and cutting operations.  In a well ventilated area, open the acetylene valve on the  torch and turn the adjusting screw on the acetylene pressure  regulator clockwise until the desired pressure is set. Close the  acetylene valve on the torch. Then, set the oxygen pressure in  the same manner by opening the oxygen valve on the torch  and turning the adjusting screw clockwise on the oxygen  regulator until desired pressure is set. Then, close the oxygen  valve on the torch handle. With the working pressures set,  the welding or cutting operation can be initiated.  Adjusting the Regulator Working Pressure Welding Tip Size Conversion Chart Wire  Drill #0 1 2 3 4 5 6 7 8 9 10 13 #000 #00 #0 1 2 3 4 5 6 Decimal  Inch Metric Equiv. (mm) Smiths™ AW1A Harris  15 Henrob/ Dillion Victor J  Series #00 #0 0.5 1 1.5 2 2.5 3 4 4.5 5 5.5 6 6.5 7 Meco N  Midget™ Foil .025 .040 .050 .063 .100 .188 .25 Aluminum Thickness (in) Foil .015 .032 .046 .062 .093 .125 .187 .250 .312 .375 Steel Thickness (in) #00 #0 0.5 1 1.5 2 2.5 3 AW200 AW20 AW201 AW202 AW203 AW204 AW205 AW206 AW207 AW208 AW209 AW210 0.150 0.279 0.343 0.508 0.559 0.572 0.610 0.635 0.660 0.711 0.742 0.813 0.864 0.889 0.940 1.016 1.041 1.067 1.092 1.181 1.321 1.397 1.511 1.613 1.702 1.854 1.930 1.981 2.083 2.184 2.261 2.362 2.489 2.692 2.794 0.0059 0.0110 0.0135 0.0200 0.0220 0.0225 0.0240 0.0250 0.0260 0.0280 0.0292 0.0320 0.0340 0.0350 0.0370 0.0400 0.0410 0.0420 0.0430 0.0465 0.0520 0.0550 0.0595 0.0635 0.0670 0.0730 0.0760 0.0780 0.0820 0.0860 0.0890 0.0930 0.0980 0.1060 0.1100 97 85 80 76 75 74 73 72 71 70 69 67 66 65 63 60 59 58 57 56 55 54 53 52 51 49 48 47 45 44 43 42 40 36 35 Figure 5-21.  Chart of recommended tip sizes for welding various thicknesses of metal. 5-12