Fastener Classification

METRIC THREAD AND GRADE IDENTIFICATION
Metric and inch thread notations differ slightly.

Common metric fastener strength property classes are 8.8 and 12.9 with the class Identification embossed on the head of each bolt. Inch strength classes range from grade 5 to 8 with line identification embossed on each bolt head as shown. Markings correspond to two lines less than the actual grade (i.e. grade 8 bolt will exhibit 6 embossed lines on the bolt head). Some metric nuts will be marked with single digit strength identification numbers on the nut face.