Head = 3-1/4 inches wide by approx 3/4" on both 235 and 261 Bottom Part of the Thermostat Housing almost the same with the difference being 1/8" in width smaller. (3-1/4' x 5/8")
Top Part Outlet a little less than 1-1/4" ID on both 235 and 261 versions of the Housings.
The internal outlet for the Thermostat Housings are the difference.. Here we find..
Bottom Part internal where the Thermostat seats: 2-1/4" ID Top Part is the same.
The 261 Housing Assembly (both parts are beefier using 1/2" NPT outlet to the Heater (or electric fan) (TRUE FOR BOTH OUTLETS) as opposed to the normal 3/8" NPT for the 235 version.
I will post pics here tomorrow once I clean these parts up a bit.
