Washers made from different materials are available in all the sizes you're likely to need to install Gyford StandOff Systems™ machined, aircraft-grade aluminum hardware.
Vinyl Washers all have 5/16" diameter holes and outer diameters ranging from 9/16" up to 2-1/4". Nylon Washers also have 5/16" diameter holes and come in 1/2" & 3/4" diameters. Timing Washers are soft 'compressable' washers that allow tightening or loosening assemblies that require parts to be in specific alignment to work. Metal Washers are available in assorted sizes that may be needed for your designs. They are typical hardware store items.