If you'll pardon the thread necromancy:

I tried to set up a Mac parts catalogue in FM (Pro I believe) but was stumped by the task of adding fields on the fly.

equill's input above suggests this was due to my own lack of clue, or a limitation of the version I was using. I know it was an old one that ran on a 68k. I had a manual which I was working my way through, but from memory, it was for a different (but roughly contemporaneous) version.

Here is the stick; clue me.