These are 21.25mm brackets to offset the servos to the correct distance with dampers in place and to get some additional dampening. Used 3D Printer Motor & Vibration Dampers that are 5.75mm in height. The long version has additional lugs on top. You would need to drill corresponding holes into the D6 enclosure. The short version replaces the standard brackets. You will need a 9/32 or 7mm drive socket to fasten the nuts. There is a screw for a cable guide below the right motor that you might have to take off /shorten to fit the bracket or use Version 2 that is altered on the right side. I printed these in Carbon Fiber PETG 5 layers all around and 50% triangle infill. They turned out very solid indeed. Still testing but print quality seems improved as vibrations are gone. The silence when printing is stunning. The family is happy......