The spacer is an M10 joining nut, drilled out half way from one end, with appropriate sized bit, and then tapped 7/16 UNF to screw on to the captive bolts in the TR TRader brackets. A good heavy wide M10 washer between the joining nut and the seat runner. I then used either 20 or 25mm M10 tapered head bolts with a washer underneath so I can fit the MX5 plastic seat runner covers.