Here's another page from the 1953 catalog that shows the Knox split bridle ring and loop style bridle ring. The large size I have would be the No. 447 and the loop style No. 446. Don't know which company has the patent for the porcelain split style ring yet, but I'm assuming probably either Knox Porcelain Corp or Porcelain Products Incorporated. The embossing on my piece is similar to the small embossed Diamond Expansion Bolt Co. piece but there porcelain parts were made by another company for them under contract.