I believe it was in 1972 when Harley introduced disc brakes. This part was used to attach the wheel hub to the rotor. Its original (OEM) and in good shape.
Look at my other listings. The item "Harley Shovelhead Front Wheel Hub To Disc Brake Rotor Adapter" is in sale since Monday, August 21, 2017. This item is in the category "eBay Motors\Parts & Accessories\Motorcycle Parts\Antique, Vintage, Historic". The seller is "50calusmc" and is located in Merrick, New York.This item can be shipped to United States, Canada, United Kingdom, Denmark, Romania, Slovakia, Bulgaria, Czech republic, Finland, Hungary, Latvia, Lithuania, Malta, Estonia, Australia, Greece, Portugal, Cyprus, Slovenia, Japan, Sweden, South Korea, Indonesia, Taiwan, Thailand, Belgium, France, Hong Kong, Ireland, Netherlands, Poland, Spain, Italy, Germany, Austria, Russian federation, Mexico, New Zealand, Philippines, Singapore, Switzerland, Norway, Saudi arabia, United arab emirates, Qatar, Kuwait, Croatia, Malaysia.