Double Take Split Clamp Assembly
https://us.adventurespec.com/shop/dtm-splitclamp-double-take-split-clamp-assembly-390
https://us.adventurespec.com/web/image/product.template/390/image_1920?unique=3cb3181
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Double Take Mirror mount split clamp assembly, 10mm x 1.25. Adapts a standard ball stud base onto any 7/8ths or any oversize 1 1/8ths handlebar.