There are two, a 180 and 185. Replace them both along with their rubber seals. There is also an O Ring on the crossover tube feeding the rear of the Thermostat Housing. Buy two, use 1. The second is a spare in case the first one gets chewed up in the swap.
Lube the first well when pushing back into the housing. Undiluted coolant will work.
I just replaced mine. There's a video on the tube abt doing it w/o disconnecting at the rear of the thermostat housing. That's the way I did it. A few more fasteners to remove and a couple of big elec connectors to disconnect but it went pretty quick.