Jerry had one of the most massive key-rings I have ever seen. My memory may be faulty, but I remember it as being a full six inches in diameter with little room left for additional keys, a real "janitor's ring." He had keys to dozens of offices, labs, classrooms, basements, roofs, athletic facilities, etc. It was too big for his pocket, so he usually wore it on an industrial strength metal key retriever that was clipped to the leather belt at his waist, where it jangled and scraped against walls and doors. At times I wondered how he kept his pants from falling down since the net weight must have been a couple of pounds.
But, although he carried this huge metal rosary at his waist, he seldom used any of them since his favorite mode of moving about the MIT campus was through the use of a "loid" He always had a couple of old credit cards, a length of plastic ruler, or a piece of twisted coat-hanger in his pocket, and there were few places that could deny his entry. He prided himself on being able to use the maze of tunnels, corridors and maintenance passages to cross the entire campus without ever going outside. He tried to teach me the tricks, but I was an indifferent student of the art, either being too clumsy or having too big a self-righteous stick up my butt.
Bearing in mind his usual attitude of never letting truth stand in the way of a good story, Jerry once claimed to have taught Amar Bose the tricks of gaining after-hours entry at the MIT swimming pool so that he could experiment with its acoustics.