M4 x 9mm OD DIN 125 Grade HV200 Zinc Finish Steel Type A General Purpose Flat Washer / CROSS-SECTIONAL SHAPE STYLE: 1 RECTANGULAR HOLE DIAMETER: 4.3 MILLIMETERS NOMINAL PERIPHERAL SHAPE STYLE: 1 ROUND CENTER HOLE SHAPE STYLE: 1 ROUND THICKNESS: 0.8 MILLIMETERS NOMINAL OVERALL DIAMETER: 9.0 MILLIMETERS NOMINAL END ITEM IDENTIFICATION: MRAP BUFFALO MK2A2 HEAT TREATMENT: HARDENED MATERIAL: STEEL OVERALL MATERIAL DOCUMENT AND CLASSIFICATION: NSI B18.22M NARROW SERIES ASSN STD SINGLE MATERIAL RESPONSE OVERALL SUPPLEMENTARY FEATURES: M4 METRIC PLATED MEDIUM CARBON STEEL