About: http://webisa.webdatacommons.org/308601772

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	Another possibility is a 3 piece design, the large concentric central holes would have been turned on a lathe, and 2 plates screwed to the outside.
http://www.w3.org/ns/prov#wasQuotedFrom	hackaday.com