Metric fasteners are similar to inch fasteners in types, head styles, drives and applications and can often be confused with their inch counterparts. Always check carefully the fastener being replaced to determine whether it is an inch or metric fastener. Metric fasteners are measured in millimeters and in the case of hex bolts or nuts have distinctive head markings and grade designations. Three metric threads ISO coarse, fine and extra-fine are found on many cars,trucks and RVs. Always match the intended replacement metric fastener to its original. Zinc plated fasteners have good corrosion resistant qualities and are a good choice for indoor and industrial applications. Property class: 8.8 (nominal tensile strength 800 MPa or about 118,000 p.s.i., similar to SAE grade 5). Class 8.8 are made from medium carbon steel, quenched and tempered. Simlar to grade 5 strength. Used in construction, machinery, automotive and other projects.