Q: What is the diameter of the face?
A: 3.25" would be the diameter of the face
Q: Does the thermometer come with a thermowell or does that need to be purchased separately?
A: This would be the thermometer only and not the thermowell, the thermowell is on part ID 30-5177A
Q: Is there a separate threaded adapter or does the thermometer itself have threads? And will this fit into the 3 gal Fastferment?
A: The thermometer does have 1/2" NPT threas on itto use to connect to the proper female connection.Unfortunately this thermometer is a bit big to fit onto any of the openings on the Fastferment 3 gallon
Q: How do you install the thermometer into the thermo well?
A: They both have threads so you simply screw the thermometer into the screw hole on the side of the fastferment itself.