All nice and well when building on a workbench, but having rubber feet would be nice to prevent a small model from marring a tabletop. And as with typewriters, prevent models from skidding all over the table. A pulley fitted with a rubber tire could be used of course, but wanted something more compact - like a collar or bushing.
So we got some made.
With the easy availability of 3D modelling software and easy access to very affordable 3D printing in rubber, getting custom feet manufactured is not only doable - it's probably even less hassle than finding the right part in the hardware store. A quick design was made in Sketchup for a half-inch round by a quarter-inch high foot and a set of these printed locally via 3DHubs in black Ninjaflex at 100 micron layer-height.
The model, trivial as it is, can be downloaded from Thingiverse here.
(The barrier to replacing broken or missing rubber feet on machines is getting lower and lower :-)