Shower turns on when stem tightened

I'm still trying to replace my shower stem...continued from here.

OK, I removed my old shower stem and brought it into a plumbing supply shop. They believe it's an American Brass and I brought the new stem home to try. It screwed into the pipe perfectly well, but when I turned the house's water supply back on, the shower was running.

It's the stem on the cold side and it tightens to the right. Would it tighten to the left as well?

Or is this an indication it's the wrong brand?

Did they sell me the wrong thing?

Or am I just overlooking an easy solution?

Thanks!

Sounds like they sold you the stem for the hot side.

Thanks. Do you think it would work if I screwed it in to the left?

Simple answer NO.

Ha OK, but maybe I tried it anyway and can confirm that you're right! I figured it out. I didn't realize that the front of the stem turned off to the left while the stem itself screwed in to the right. Amateur.

Well this was a big step backwards for women attempting DIY projects overall, but I got it done. Thank you for your help!