This listing is for a set of 4 rollers that replace the larger rear rollers on Underwood F Model Universal Portable typewriters. These likely fit other similar models. The smaller front rollers are also available in my shop. 

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. 

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.