7/16" Left Hand Lug Stud
I could never justify the LH threads and the reasoning behind that.
I spent a lot of time searching for, not a screw and bolt, but "THE" screws and bolts for my 66 Coronet. I wanted it to be exactly as it rolled off the line. There were a few exceptions that I granted myself, dual master cylinder brakes (for obvious reasons), 15" wheels...but I didn't think twice about ****-canning the left hand studs, though. I got rid of every dam one. That's probably why one of yours is broke...some mechanic went the wrong direction.
You can get these "lefties" from Rock Auto. If it's only you turning the lug-wrench from here on out, perhaps you're safe enough. But sure as ****, there's a mechanic that never heard of LH wheel studs.
I recently went to an auto parts store for brake banjo bolts and the counter guy told me to use Ford bolts...because Chrysler is made by Ford.
Another 20 years of this, I'll be dead and free of all this insanity.