HLB-4 HEICO Fastening Systems HEICO-LOCK Washers , Manufacturer Part#: HLB-4 , Manufacturer: HEICO Fastening Systems , Brand: HEICO-LOCK Washers , UOM (Inch or Metric): Metric , Material: Steel , Finish: Zinc-Flake Coated , Bolt Size: #8 UNC (M4) , Inside Diameter: 0.170 Inch (4.40mm) , Outside Diameter: 0.350 Inch (9.00mm)