module prism(l, w, h) {
       polyhedron(points=[
               [0,0,h],           // 0    front top corner
               [0,0,0],[w,0,0],   // 1, 2 front left & right bottom corners
               [0,l,h],           // 3    back top corner
               [0,l,0],[w,l,0]    // 4, 5 back left & right bottom corners
       ], faces=[ // points for all faces must be ordered clockwise when looking in
               [0,2,1],    // top face
               [3,4,5],    // base face
               [0,1,4,3],  // h face
               [1,2,5,4],  // w face
               [0,3,5,2],  // hypotenuse face
       ]);
}

threadDiameter = 7;
threadTubeOuterDiameter = 11;

baseThickness = 4;
baseHeight = 40;
baseWidth = 80;

gapWidth = 30;
clampDepth = 15;
clampHeight = 10;

difference() {
  union() {
    cube([baseThickness, baseWidth, baseHeight]);
    
    translate([-clampDepth, 0, 0])
      prism(baseWidth, clampDepth+baseThickness, clampHeight);
    
    translate([0, (baseWidth - threadTubeOuterDiameter)/2, 0])
      cube([threadTubeOuterDiameter, threadTubeOuterDiameter, baseHeight]);
  }
  
  // thread hole
  translate([threadTubeOuterDiameter/2, baseWidth/2, 0])
    cylinder(r = threadDiameter/2, h = baseHeight);
  
  // clamp gap
  translate([-clampDepth, (baseWidth-gapWidth)/2, 0])
    cube([clampDepth, gapWidth, clampHeight]);
}