Pocket Watch Molds

I need help finding a word that best fits this description … Help?

OK, I got the word earlier, now it just slipped my mind. It's like you want to shut the door all the way, and theres that long queues little opening between the door and molding. Or when you're seeing if a box opens, but you do not see a _______ If Or If you see a pocket watch opens, but you see ________ not showing it could open. I hope you guys get the idea. Im thinking away, but thats not … my breathtaking his mind now. Crack described as something broken ajar might work, but not what I'm looking for. The other is away. This not sewing … sewing is sewing.

crack?

Fiberglass Door Panel: How to make an RTV Rubber Fiberglass Mold of a Door Panel Piece (Part 2)