A hard-drawn spring steel extension spring is to be designed to carry a static load of 18 lbf with an extension of ½ in using a design factor of ny = 1.5 in bending. Use full-coil end hooks with the fullest bend radius of r = D/2 and r2 = 2d. The free length must be less than 3 in, and the body turns must be fewer than 30. Integer and half-integer body turns allow end hooks to be placed in the same plane. This adds extra cost and is done only when necessary.