(200pcs) 3/8'-5/16-18x2 3/4' UNC Socket Shoulder Screw, Alloy Steel, Thermal Black Oxide, (inch), Size: 3/8'-5/16-18, Length: 2-3/4', Coarse Thread (UNC), RoHS: Industrial & Scientific. (200pcs) 3/8"-5/16-18x2 3/4" UNC Socket Shoulder Screw, Alloy Steel, Thermal Black Oxide, (inch), Size: 3/8"-5/16-18, Length: 2-3/4", Coarse Thread (UNC), RoHS: Industrial & Scientific. Black Oxide Finish is a conversion coating (not an applied coating) because it results from a chemical reaction with the iron present in the metal fastener and forms and integral protective surface. It is a color of the base metal, which neither removes nor deposits metal; therefore it adds, at the most, 5 to 10 millionths of an inch to the fastener’s dimensions. Likewise, it cannot chip, peel or rub off. Also, the item maintains 99% of its conductivity making black oxide a popular finish for electrical parts. When a black oxide finish is specified, it is interpreted as “Black Oxide and Oil”. Typically, the oil after-finish is dry to the touch, which gives the part a lustrous appearance and improved lubricity without excessive residue. The color is a deep black rather than the grayish-black appearance of a black phosphate, and remains consistent at temperatures as high as 900ºF. Black oxide also resists abrasions better than phosphate. One of the most important advantages of black oxide is that there is almost no risk of hydrogen embrittlement because the process does not involve electro-plating nor does it require an acid-activation. Black oxide neither enhances nor detracts from a fastener’s resistance to corrosion. The post-treatment oil application offers good indoor corrosion protection, but a zinc-plated part is more resistant to rust. However, parts with a black oxide finish will not suffer from white corrosion, which can occur over time with electro-plated parts. To avoid the risk of white corrosive particles (which can cause electrical shorts) many in the electronics industry opt for black oxide instead of zinc plated fasteners. The popularity of black oxide stainless fasteners is also growing. In addition to being used for decorative purposes, the finish reduces light glare and reflection, and makes the surface of the fastener smoother . . .