Thank you for submitting your items for appraisal. These appear to be three vienna bentwood "tilting office armchairs", manufactured circa 1910, a variation of the catalogue number 704. Near identical are listed in the 1910 Jacob & Josef Kohn catalogue. Due to changing workplaces various attempst were made during the early 20th century to improve office chairs. This version is one of many designs by different manufacturers. Surprisingly I couldn´t find any auction results or current offers for this chair. This is a mass produced chair, but it could be rare today. The estimate is based on similar office or bentwood chairs sold at auction. Currently there is no price to compare with, the current auction result might be higher if offered at auction.