QUOTE:
The Rubner Roll rollers
(optional, use the "Select roller style for pricing") pull down box have a bearing on the end of the roller that fits in the center section of the headstock. These rollers eliminate the roller binding on the wood of the headstock, the tuners are literally as smooth as Gotoh 510 sealed tuners (for steel strings).
This shows them:
https://www.rubnertuners.com/new-page-3/
I bought a set of the Rubner Rollers... and wow, they are smooth and perfect for a lovely little classical parlor guitar I bought.