| 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. |
| Activation | (english) The changing of the passive surface of a metal to a chemically active state. Contrast with passivation. |
| 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. |
| Acute Angle | (english) An angle that is less than 90 degrees. |
| 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. |
| Adapters | (english) Steel segments that are bolted to the reel mandrel to increase their diameter so that large (24" ID) coils can be run. |
| 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. |