This detail outlines when washers are required and when they are not needed.

Simply put, for both A307 and A325 Structural Hardware a washer is only required when installed to a slotted hole. If the hole in the part is not slotted a washer is not necessary but can be used.

Note:

While A325 bolts have similar properties to Grade 8 bolts, they do not require a washer when installing through holes. The head of the bolt and the nut are oversized compared to non-structural bolts, this provides a larger contact area between the bolt and the steel substrate.

Click here to view a PDF drawing of SD11