What should you check before choosing washers for outdoor wood or metal assemblies?
A lot of people choose bolts carefully but ignore the washer. In many assemblies, that’s where problems start.
For wood, the washer helps spread the load so the bolt head doesn’t crush into the surface. For outdoor use, coating matters because a rusty washer can weaken the connection even if the bolt itself still looks fine.
For metal assemblies, washer hardness and thickness become more important. A very thin washer may deform under load, especially when used with higher-grade bolts.
My usual checklist is:
material, washer type, inside diameter, outside diameter, thickness, hardness, coating, working environment, and whether the hole is oversized.
For standard jobs, flat washers or fender washers are usually enough. For vibration, spring washers or other locking solutions may be considered. For special equipment, a custom washer may be needed if the OD, thickness, or material is not standard.