Removed a bottom bracket that was rough and rusted. Went to the bike Co-op and picked up a suitable replacement. I did not get a non-drive side cup since I had a couple at home.

I installed the bottom bracket, drive side first without issue. I could not get either of the NDS cups to thread in. I removed the bottom bracket and was able to thread in both NDS cups without any problem. Tried to slide the cups onto the bottom bracket and they will not slide on, they are too small, about ½ a mm. Tried the cup I had just removed and it will not fit either of the bottom brackets (“new” or old).

I’ve installed a few bottom brackets and never had this issue before. I thought these were interchangeable.

Anyone ever had this problem? I’m about to order a new one but thought I would post this first. Thank you.