21 lines (15 with data), 359 Bytes

//this fiel will draw a cylinder along the main axis of the joint
ref1={
  
  AnyRefNode ZCyl={  
    sRel={0,0,-cyl.Length*0.5};
//    ARel=RotMat(pi*0.5,y);
    
    AnySurfCylinder cyl={
      Radius=0.001;
      Length=0.02;
      AnyDrawParamSurf surf={
        Opacity = 0.1;
        RGB={0,0,0};
      };
    };
  };
  
}; //ref1