washer HV
washer A2
which is described as follow
HV washers are hardened and tempered washers and are used where higher load and tightening torque is required to tighten the bolt or stud bolt with the nuts. HV washers provide higher strength and enable friction coeffeicient between tightened stud bolt & nuts.
and A2 washer:
A2 Grade Stainless Steel Form B Washers (DIN 125 B) are thinner than a Form A Washer. Smaller sizes up to M16 sold in packs of 100, larger sizes in 50's and 25's
In general, many times use a flat washer under a split locking washer to protect the base material, plating, or coating from damage caused by the split washer action. We may also use the flat washer to distribute the fastener load or ensure the split washer does not fall or grind into a larger clearance hole feature.
Flat and lock washers are two of the most common types of washers. A flat washer is a basic washer that's flat on both sides. A lock washer is a semi-coiled washer that's used to secure bolts .in place