Outer Diameter. It seems fairly safe for me to assume that the replacement washer you have in mind has the same inner diameter as the one you lost and will fit correctly around the screw. But hey, you never know.
East Coast Park Rat
2008 Burton Twin 157 w/ Rome 390 Boss
2005 Burton Canyon 168 w/ Ride LS
"its ppl like you, that I would "impact damage" your face if i ever saw you
keep your mouth shut. one more time, please and thank you." -user: chingy_