"Small" part info request for T85

[Doug Johnson]

On my '86 4kcsq, down below the antenna in the fender area, there's a green
plastic canister mounted in a vertical position........with no securing
screw.  The top anchor is a press-fit "knob," but the screw at the bottom is
missing.  I can't find the canister in FP, but could someone please tell me
a size for that screw, and is it backed up by a flat and/or a clocking
washer?  Also, what's the canister......is it related to the fuel system?

TIA,

~ Doug