I simply use bits of paper handkerchiefs or similar to fill gaps and tighten fits. Plenty available, doesn't damage anything. If you feel artistic you could even make papier-maché out of that paper.
A trick from the model builders world would be to take the closest fitting peg, heat it (gently) and then squeeze it around the neck ball.
Note I didn't try this myself, I'm waiting for a guinea pig.
A trick from the model builders world would be to take the closest fitting peg, heat it (gently) and then squeeze it around the neck ball.
Note I didn't try this myself, I'm waiting for a guinea pig.