Boy With Autism Hits Himself when He Sees His Hands

--> I work with a 6-year old boy with autism who hits himself violently in the head whenever he sees his hands.  Over the summer the boy's mother put weights on his hands and the boy didn't hit himself when he was wearing the weights.  Now the weights don't work, the only thing that works is if the boy has a blanket covering his hands.

If the boy has a blanket over his hands he is able to play, utilize his hands functionally, and not hurt himself.  If the boy has mittens on he hits himself.  If the blanket is held above the boy's hands he does not hurt himself but will utilize his hands functionally. 

Anyone have any ideas??  This child needs help.