You can buy a WP3949550 3949550 8544817 rubber aggitator bolt washer online for $10 to $20 shipped for a single washer, but this seemed silly to me. Looking online, I couldn't find anywhere the exact dimensions of the washer so I could just get one from McMaster-Carr or Grainger.
So I spent the $15 and bought one and took measurements of it (so nobody else has to).
The washer is a rubber washer that has
- OD Outer Diameter : 18.6mm : 3/4" : 0.7344"
- ID Inner Diameter : 7.2mm : 5/16" : 0.2813"
- Thickness : 2.5mm : 3/32" : 0.0984"
McMaster-Carr sells this washer for $11 for 10 of them : https://www.mcmaster.com/93650A117/
It has OD 0.750", ID 0.281", Thickness 0.085" to 0.101"
Here are some photos of the measurements and of the washer I got (not from McMaster-Carr)


