putting thermowells in my MT

I've got to a place where I'm thinking about the MT and temperature control.

The MT is an 80 QT SST pot.  I can drill it and weld in pretty much what ever I need.
But, I don't know much about thermowells and their relationship with Thermometers and Thermocouples.

Do I need a thermowell for a thermometer?
If so how do I think about  the depth/length relationship  between the thermowell stated length and the stated length of the thermometer stem?

What about the thermocouples. Maybe a swagelock like pass through into the thermowell for that with some heat transfer grease in the well?

Never done it before, so I'm at zero here.

Answers:
Yes you should use a thermowell  with a thermometer and match the stem length to the thermowell length - there will always be a little extra room in the thermowell where you need to place a bit of conductive grease.

Some thermocouples (TC) will be spring loaded so you can get point contact in the bottom of the thermowell but you still need the conductive grease.

The reasons not to simply insert the thermometer probe into the mash tun or brew kettle are:
1.) You can pull it out without losing your wort or beer.
2.) there are vibrations that interfere with a thermometer's reading  from flowing fluids  The thermowell helps eliminate this.
3.) you can damage the thermometer by impacting it with a paddle, while cleaning,  or get things like hop bags and crap hung up on it.  the thermowell is sturdier and won't bend or break.

Match the thermowell length to the depth of the  stem  4" with 4"  and you should be golden.  the variation caused by the depth of engagement from the NPT threads won't be sufficient to cause you to jam the end of the thermometer into the bottom of the thermowell.  They make 'em with enough extra room.