OpenSCAD source code: Tour Easy Zzipper Fairing mount bracket

Fairing Flashlight Mount.scad: Bracket excerpt

//- Fairing Bracket
// Magic numbers taken from the actual fairing mount
// Centered on screw hole

/* [Hidden] */

inch = 25.4;

BracketHoleOD = 0.25 * inch;          // 1/4-20 bolt holes

BracketHoleOC = 1.0 * inch;           // fairing hole spacing
                  //  usually 1 inch, but 15/16 on one fairing

Bracket = [48.0,16.3,3.6 - 0.6];      // fairing bracket end plate overall size
BracketHoleOffset = (3/8) * inch;     //  end to hole center

BracketM = 3.0;            // endcap arc height
BracketR = (pow(BracketM,2) + pow(Bracket[1],2)/4) / (2*BracketM);  // ... radius

module Bracket() {

  linear_extrude(height=Bracket[2],convexity=2)
    difference() {
      translate([(Bracket[0]/2 - BracketHoleOffset),0,0])
        offset(delta=ThreadWidth)
          intersection() {
            square([Bracket[0],Bracket[1]],center=true);
            union() {
              for (i=[-1,0,1])                    // middle circle fills gap
                translate([i*(Bracket[0]/2 - BracketR),0])
                  circle(r=BracketR);
            }
          }
        circle(d=BracketHoleOD/cos(180/8),$fn=8);     // dead center at the origin
    }

}

More details on my blog at http://wp.me/poZKh-6UL