ASME B18.2.1 UNC HEX BOLT GRADE 5 BLACK OXIDE INCH SIZE 1/2-13

UNC refers to the coarse thread in the United States unified thread UN series (optional external thread root radius).

What"s the Black Oxide surface treatment?

Black oxide, a common means of chemical surface treatment. Black oxide is a common method of chemical surface treatment. The principle is to produce an oxide film on the metal surface to isolate the air and achieve the purpose of rust prevention. When the appearance requirements are not high, blackening can be used, and the surface of steel parts is blackened, which is also called blue.

The commonly used methods of black oxide treatment include traditional alkaline heating blackening and room temperature blackening which occurs later. However, the blackening process at room temperature is not very effective for low carbon steel. Alkaline blackening is subdivided, and there is a difference between once blackening and twice blackening. The main components of blackening liquid are sodium hydroxide and sodium nitrite. The temperature difference required for blackening is not large, and a good surface can be obtained between 135-155 °C, but the time required is a little long.