A professional from San Francisco CA area says:
August 17, 2016
spring and bearing go in through the back so you can adjust the bearing and it will roll
Tom from SWISCO responded:
August 19, 2016
I'm not sure if we can get this exact part, it looks very old. What is it used for? Is this a ball catch for a closet door? If so, could you use something like our 10-057?