What is this threaded radiator connection?

[gwb72tii]

On the RH side of the radiator:

 

 

[Mike W.]

It's an A/T radiator, it's for the auto box cooling. There should be another one below it.

Many, including myself at times, have used A/T radiators in manuals if cheaper or more available. Other than perhaps cosmetics, it does no harm.

[gwb72tii]

Do they need to be capped off?

[Mike W.]

Do they need to be capped off?

No. Only reason might be cosmetic, and even then I would vent it.

[Blue Shadow]

No.  It is just the in and out of an enclosed space inside the radiator where the tranny fluid is cooled on the auto box. Capped would probably look better, more attention to detail and it would preserve the rad for auto use by keeping dirt out.