Gardner Ultra Precision Extension Springs are made to strict tolerances from high-grade materials. Tight quality control is maintained throughout the manufacturing process. Ends are full twist loops. Ultra-Precision Extension Springs have an excellent fatigue life and many sizes are ideal for dynamic or heavy cycle applications. Other uses include maintenance, prototyping, and equipment repair. All parts are stress-relieved. Parts have plain finish and are available in Music Wire (ASTM A228 and AMS 5112) or 302 Stainless Steel (ASTM A313 and AMS 5688).