Thats the whole truth and nothing but the truth. Most any other thermostat may fit but they just are not the correct thermostat. Use another thermostat and you take your chances. I personally always heat up the thermostat in a pan of boiling water and actually measure the opening gap. If it wrong I can make a small adjustment but thats about it. They really need to be correct from the factory. I also cut off the rubber positive closure part of the rubber gasket around the sealing area. I leave the part that glued to the body of the stat. I feel I get more flow thru the factory thermostat that way....