the little spacer was surefires temporary fix for the oring
in the original design, there was no spacer and so there was a little gap where the clip was
as a result, the oring when compressed could squish in there and lose water resistence
surefire first issued a little plastic spacer,
then they resorted to issuing a flat washer that sits over the gap
i have an e2e that was an old one, didnt have a plastic washer or plastic spacer
then e20, this had plastic washer
then L4 body, this didnt have plastic washer / spacer
then e2D body, this has the plastic spacer
as far as i know, i think surefire didnt continue making it with the little plastic spacer and moved onto a plastic washer
the plastic spacer fits into the hole
the plastic washer fits over the hole
hope this helps