During discussions with the customer, different attachment ideas and materials were suggested--brass or aluminum were the customer's first choices. The tightening torque for securing to a nut was to be 12 lb/in. After sketches were sent back and forth, samples were sent for test and evaluation. This particular application called for a material not normally used by Helical--copper impregnated with aluminum (Glidcop, AL60). After a long test and evaluation program, the proposed spring was approved and production started.