Large main spring of some sort, new old stock. We initially thought it was for a movie camera but we now think this is for a large clock. Measures 3.5" across as shown, band material is 7/16" wide. 

WHO WE ARE: Oddog2 is a husband/wife team, home-based small business specializing in the buying/refurbishment/selling of primarily photographic equipment. We do occasionally have other types of things to sell that come to us as a result of our search for camera-related items. We have 47 years of experience (22 years as a hobby, 25 as a full time effort) with photographic equipment, both as a shooter (17 years newspaper photojournalist) and as a collector/restorer/seller. We have been on eBay as Oddog or Oddog2 since September 1999.