This 6mm D-Bore to 8mm REX bore Hyper Coupler is a strong, compact, balanced way to couple two shafts together. Maybe you have motors with 6mm d-shafting but you want to step up your game and run 8mm REX to handle higher torque loads. Maybe you’re going the other way due to a surplus of 6mm D-bore pinion gears, hubs, sprockets, etc. The diameter of the coupler has been thoughtfully chosen so that, when installed, you can still access screws on the 16mm pattern with the use of a hex key. The length is such that, when a motor with a 24mm length shaft is installed perpendicular to 1120 Series U-Channel, the coupler can slide in between the end of the shaft, and the inside wall of the U-Channel. And as with all ‘Hyper’ parts, this too is balanced so you can spin it up without concern of creating unwanted vibrations through your drivetrain.