These are the plastic rollers on my horizontal windows. The house was built in 1988 when these windows would have been installed.
There are no markings on the part. The one pictured is the last spare that I have.
Dave Sr. from SWISCO responded:
August 24, 2016
We could not come up with an exact replacement for your roller, unfortunately. However we do have two that are similar that you may want to consider, our 87-008 and 87-120. Could you adapt either of these to work in your window?
A quick learner from ID says:
April 22, 2020
I don't know if the original poster will see this response, but this is the part I'm looking for too! If you do see this, did you have any success in finding a replacement?