A Gauge to MM plug conversion chart that doesn't skip sizes : r/piercing
inch to mm convert | 1/2 or 3/8 or 3/4 inch to mm - YouTube
Metric Conversion Chart | Fastenere.com
Amazon.com: Vacuum Cleaner Adapter 35mm (1-3/8 Inch) to 31 mm (1-1/4 Inch) for Inner Diameter 32 mm Brush Fit to Outer Diameter 35 mm Tube Plastic Vacuum Hose Adapter(2 Pieces): Home & Kitchen