Countersunk Bolts Machine Screws Metric Fasteners 12.9 Grade Bolt

Countersunk bolts with a conical hole cut into a manufactured object, or the cutter used to cut such a hole. A common use is to allow the head of a countersunk bolt or screw, when placed in the hole, to sit flush with or below the surface of the surrounding material (by comparison, a counterbore makes a flat-bottomed hole that might be used with a socket-head capscrew). Ever Hardware provides custom-made fasteners and customizable packaging.

12.9-grade steel bolt means that a component manufactured form this grade of steel has 12X100 N/mm^2 tensile strength and 9 is a multiplier means 90% of 1200 = 1080 N/mm^2 is the yield strength of the grade.
Similarly, we also have grade 8.8, 10.9, 6.8 also. This is an imperial method implied by engineers to differentiate between different sets of steel grades. The bolts are mainly used to differentiate the bolts and nuts. like Grade 12.9 Hexagonal Bolt.

Phosphate coatings are a crystalline conversion coating that is formed on a ferrous metal substrate. The process of Phosphate coating is employed for the purpose of pretreatment prior to coating or painting, increasing corrosion protection, and improving friction properties of sliding components. In other instances, phosphate coatings are applied to threaded parts and top coated with oil (P&O) to add anti-galling and rust inhibiting characteristics.
The phosphating process relies on the basic pickling reaction that occurs on the metal substrate when the process solution comes in contact with the metal.

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