This is a conversion throat that fits JBL's 1 inch and 2 inch screw holes. The manufacturer is unknown, but it is made of solid metal. There is paint loss on the mounting surface (Murakoshi Yoichi)
Accessories: none
Main specifications: opening 1.5 inch side 51 mm, 1 inch side 38 mm, outer diameter 120 mm, height 50 mm