Crossover center loop extension springs have fully enclosed loops on their ends rather than hooks. Also called full-twist loop extension springs, they are often used on smaller springs.

Machine hook extension springs are formed with easy-to-install hooks on both ends. Also known as half-loop extension springs and extension springs with hook ends, they provide reliable strength, withstand repeated stretching, and are often used for larger springs.

Double-loop extension springs have ends with two coils for added support and strength to help eliminate breakage. They are often used in automotive systems and industrial and commercial machinery.

These assortments contain numerous springs of different materials and various lengths.