casters

[Michael Kurta]

    You can wrap the stem with some sort of material to create a tight fit 
in the socket, but it may not be reliable.  They usually do use a spring 
type collar fitted in a groove to hold the stem in place.  I try to save and 
reuse these from old casters, and I've made some up from the right diameter 
coil spring, but its a bit tricky.  Your best bet might be to just replace 
the offending caster assemblies.
    Mike Kurta