Hard drawn 18–8 wire, when heated above 800°C., suddenly loses its mechanical properties. As it is impossible to harden it by heat treatment, it is necessary to perform the soldering operation at a temperature below 800°C. In such cases, it is possible to restore its mechanical properties in a large measure by twisting the wire near the joint, as 18–8 possesses the property of rapidly hardening when cold worked (Fig. 1). Spot welding is suitable only when the thickness of the band or flange more or less corresponds to that of the sheet to which it is to be welded, and should not be used to join auxiliary springs and arch wires. One kind of electrode is ample for spot welding in the construction of orthodontic appliances. Hard drawn wire should be moderately hard, although this differs according to the diameter of the wire. Seamless flanged tubes are more useful and give better results than tubes made by pressing. The Ellis type loop lock must be hammered to make an accurate and cleanly shaped shaft. When making orthodontic appliances of 18–8, buffing and pickling are unnecessary, if not inexpedient. The scraper and the pumice stick are sufficient when polishing. When using an appliance made of 18–8, it is necessary fully to understand its properties and to employ the most suitable heat treatment.