Hi Fred
Someone here with a decoder may come by, and can identify the year and month of manufacture of your machine.
At a glance.. Il take a guess that it's a 1966. The black agitator may be a replacement from a older machine. If it is a 1966 model...it would have come with a aqua colored agitator (same color as your release bar)
The T bar on top of the wringer.. I think you referring to the tension bar. Maximum tension is used when fabric is being run through the wringer. When finished the release bar is used to release tension and to separate rollers so their not touching during times when the machine is not in use. This is done in order to avoid getting flat spots on the rollers.
I can't tell from the pic if your machine is a pump model or not.
Feel free to ask more questions. If you have never used a wringer, you'll need us! LOL
Hope this helps