OK, question.
How do you define hardened? When I look at Grainger's site for internal/external washers, I find the following (2 examples linked):
Lock Washer, Int/Ext, 0.267 ID, PK100 - Lock Washers - Washers - 2DB80 : Grainger Industrial Supply <--1/4"
Lock Washer, Int/Ext, 0.398 ID, PK100...