The NAPA THM155 thermostat has a 2.5" diameter. It is 180 degrees. Here is a link to pictures showing the thermostat and how it sits in the upper and lower 261 bypass housing. I also took pictures of the NAPA box showing the specs and the UPC code.

http://s844.photobucket.com/user/ma...1367_zps84yrah8s.jpg.html?sort=3&o=0

Matt

Last edited by Maybellene; 03/14/2016 2:29 AM.