UE4’s PBR uses information that you supply about certain properties to accurately determine what it should look like. The “Metallic” input tells the engine how metal-like it is. You’ll need a simple node network connected to Metallic, since I assume that your fire extinguisher is mostly metal. 0 means it isn’t metal, the closer to 1 the more metallic; you can adjust it with your texture and a Lerp node. Next you should disconnect specular and leave it alone, you should leave specular at default for metals or anything that behaves like one. Roughness is just what it sounds like, setting it to 0 will result in a perfectly smooth surface, a higher value will be rougher and light will be scattered. For the roughness, you can use a linear interpolate to vary the roughness between two values for different parts of the object based on the texture. This link is very informative and will help you understand what everything does. Study the Roughness section and play with the slider, it will help you achieve the results you want in conjunction with the metallic input; most of your mesh will need a roughness value in the higher range to look correct.