High quality brass thread adapter M8 to M4 / M6 / M8 / M10 / M12, set of 4 | eBay
Mirror Adapter M10 x 1.25 Left Hand Thread to M8 x 1.25 - HIGHSIDER
Uxcell M10 Male to M8 Female Adapter 10mm Long Sleeve Reducer Thread Reducing Nut Insert 5 Pack - Walmart.com
10pieces/lot M6/M8 to M10 threaded hollow tube adapter inner outer threaded coupler conveyer adapter total length 15mm - AliExpress
1PZ MXM-001 Mirror Mount Adapter - M8 female to M10 male or 8mm to 10mm Chrome Replacement for Honda Custom Cafe Chopper Bobber Tracker Vintage Classic Kawasaki Yamaha Suzuki (Pack of 2)