Thermostat O-ring

[camron at worldaccessnet.com (Camron D. Crouse)]

And while I'm on the subject of thermostats, my new thermostat (German) 
was sold along with a rubber O-ring, as if to fit against the 
waterpump/thermostat (likely) OR thermostat/thermostat housing (less 
than likely). 

But uh, the old thermostat had no O-ring. 

The new O-ring seems like it's either a tad too small or a tad too large 
to snug up against the indentation of the thermostat very well.  Anyone 
know what the heck is going on here?

Thanks!

- Camron from Vancouver, WA USA
   '86.5 Black 16V 2.0L