| Acid Process 2 | (english) A steel making method using an acid refractory-lined (usually silica) furnace. Neither sulfur or phosphorus is removed. |
| Acid-Brittleness | (english) Brittleness resulting from pickling steel in acid; hydrogen, formed by the interaction between iron and acid, is partially absorbed by the metal, causing acid brittleness. |
| Acid-Process | (english) A process of making steel, either Bessemer, open-hearth or electric, in which the furnace is lined with a siliceous refractory and for which low phosphorus pig iron is required as this element is not removed. |
| Acme Thread | (english) A screw thread having a 29 degree included angel. Used largely for feed and adjusting screws on machine tools. |
| Actual Weight | (english) The customer buys by the actual (scale) weight of the steel. The theoretical weight is used in estimating, however, it is not to be used for billing. |
| ACTUATOR | (english) A device for converting hydraulic energy into mechanical energy, i.e., a motor or cylinder. |
| ADAPTER | (english) A mechanical device used to align the shaft of an electric motor (or other rotary device) with the shaft of a hydraulic pump to maintain radial and parallel shaft alignment. |
| Adapti Investment Casting Process | (english) A lost wax process employing one of three methods; centrifugal, vacuum or gravity-pouring casting. |
| Addendum | (english) That portion of a gear tooth that extends from the pitch circle to the outside diameter. |
| Addition Agent | (english) 1) Any material added to a charge of molten metal in bath or ladle to bring alloy to specifications, 2) reagent added to plating bath. |