Slide guide, cable holders, calipers and cable guide are preferably made of aluminum, and most preferably is die-cast aluminum. However titanium and nickel bearing steels are also satisfactory. These omponents can be formed, investment casted, forged, stamped or machined. Nuts, bolts and mounting studs are preferably made of machined carbon steel . Flat washers are preferably made of nylon or other low friction materials which are extruded. Torsion springs are preferably made of high tensile steel, but piano wire and high carbon alloy steel are also satisfactory.