1970/80′s Children’s Book – Magic, Something About A Metal Washer?

Hi!
does anybody know/remember a series of children’s stories from the 1980′s (i read them late 80′s, early 90′s) that involved a young boy, a silver metal washer that was magical and allowed him to visit ‘other realms’ i think… it was very escapist; i think he lived in a horrible city and this washer allowed him to visit other, magical, green places (i remember one story that involved a lake in a wood)… from the drawings i remember they were 70′s influenced….they wernt very long and paper back from my versions i read at school.
i just really enjoyed them and i’d like to figure out what they were!!!
thanks!! hope i can get to the end of this cuz it’s really going to bug me!!! x