3 questions regarding parts (build)

Does anyone know if this
5/16-in x 1-1/2-in Stainless Steel Standard (SAE) Fender Washer will work for the 5/16 Fender Washers?

Does anyone know where to get a 5/16 x 7/8 coupling nut?

Are all the screws/bolts hex, philips, hex socket, slotted? (based on the build there seems to be a mixture of hex and philips, can anyone confirm this type or does it not matter?

Fender washer will work.

The coupler you should just go have a look at your local hardware store there are short and long ones, we use the short (long will work but not in the new upcoming parts).

Screw type does not matter.

Better to buy from vicious, but, you’ll have an easier time finding it at ace than the big box home stores…