This listing is for a set of 3 rollers that replace the smaller front rollers on Underwood No.4 and No.5 desktop typewriters. Check my shop for the rear larger rollers. The majority of Underwood desktop typewriters have the same size rollers just depends on the width of the platen on how many rollers you will need. Fits nice and snug on your original bare metal rollers. You will have to strip yours if there is still rubber material on them and these slide over and are very tight. 

3D printed with synthetic rubber-like material. Does not include the metal inserts. Some pictures include the metal insert to show how they fit.

I have been restoring vintage typewriters for over 6 years and the biggest pain is dealing with the old rubber rollers deteriorating. Decided to try 3D printing replacements for myself and they work great! Very sturdy and durable, great grip, and no scuff marks on the paper.