Metal spinning machines are used in metal spinning (spin forming, flow forming), a process by which a metallic disk or tube is rotated at high speeds and formed into an axially symmetric part. Typically, metal spinning machines are used to produce metal parts shaped like bowls, cans, cones, domes, donuts, hemispheres, ovals, and rings. Spin forming and flow forming equipment is also used to produce hourglass shapes, ribbed metal parts, and products with critical tolerances for wall thickness and concentricity. Specific applications for metal spinning machines include the production of air diverters, bearing cages, bells, collars, containers, covers, end caps, horns, housings, lids, shields, tanks, and tank heads. There are several main types of metal spinning machines. Hand spinning equipment and manual metal spinning machinery is suitable for shorter production runs and applications that require greater operator control. CNC metal spinning machines incorporate computer numeric control (CNC) to achieve shorter lead times, longer production runs, and more complex designs. Hot metal spinning machines apply high heat from a torch while metal blanks are spun. As the metal is heated and shaped, tooling attached to the lathe is used to narrow the neck to a smaller diameter and provide a seamless shoulder. Handheld tools called spoons are used in manual spinning processes, and powered rotating tools are used in CNC metal spinning machines. Typically, metal spinning machines are used to spin aluminum and steel. Annealed aluminum is relatively soft and elastic. Hardenable aluminum is denoted with an H and thermally treated aluminum is denoted with a T Stainless steel is more elastic than aluminum, but requires greater force to form. Metal spinning machine are also used to form metal parts from copper and brass. Copper is very formable and provides excellent elongation, but may harden before the part is spun completely. Brass is similar to copper, but exhibits less work-hardening. Suppliers of metal spinning machines may recommend specific types of equipment based on the materials to be spun. Metals such as silver, gold, titanium and magnesium may require special production considerations. CNC metal spinning machines, manual metal spinning machines, and hot metal spinning machines carry specifications such as maximum blank diameter, distance between centers, longitudinal force, transverse force, number of wheels, and rated speed. Blank diameter and distance between centers is often specified in millimeters (mm). Longitudinal force and transverse force is measured in kilonewtons (kN). Choices for wheels include single-wheel, double-wheel, and triple-wheel metal spinning machines.