any tips to stop child chewing?

[exmrs]

Son is 6 and possible Aspergers he constantly is chewing clothes, coats even sat on the settee he is chewing the corner of cushions or a throw.
He seems to like pulling a thread from whatever he is chewing with his teeth.
He doesn't even know he is doing it half the time but I cannot afford to replace any more coats and I cant find a way to stop him doing it

Try nail bite stuff on hard surfaces. Dd managed to chomp through metal frame glasses. This stuff reduced damage on next pair. Keep topping it up though so it doesn't wear off