I put the microfiche in my reader and studied page 92-4. PN #55417-E4100 washer-special D is not shown. Also not shown is the nut that goes with the hex bolt (key #20). If you look at the bolt, corresponding washers and visualize the hex nut which is not shown, it is fairly easy to see how a D washer would fit under the hex nut. I will look through my hardware which I labeled and cataloged to see if I have the "special D Washers". Of the hex bolts and washers Key # 20, # 21, #22, 4 of each were used up to 07/73 and they were changed as of 08/73. My microfiche is the latest revision (Dec 79) and there is no further mention of PN #55417-E4100 or replacement. I think it is just a flat washer filed flat on the side to fit. PS - It is key # 15 on my microfiche, not 13 like in Mike's hardcopy, or did you mistype?