The most common type of spring is a Coil Spring or Helical Spring, used to store mechanical energy and subsequently release it. These Coil Springs can be closewoundor open-wound and are made of hardened steel. The most common types are: Compression, Extension and Torsion

COMPRESSION SPRINGS can be found in ballpoint pens and valve assemblies as well as thousands of other places. When you put a load on the spring, makingit shorter, it pushes back against the load and tries to get back to its original length. Compression Springs may be cylindrical, conical, tapered, concave or convex inshape. The changing of spring ends, direction of the helix, material and finish allows a compression spring to meet a wide variety of special industrial needs; they arethe most common spring configuration and are usually placed over a rod or fitted inside a hole.

There are four basic types of compression spring ends, affecting the solid height, free length and other characteristics of the spring:

Open Ends, Not Ground: the ends of a compression spring are opened with a constant pitch for each coilOpen and Ground End: the ends of the spring are open and ground creating a flat surface
Square or Closed Ends (SQ): the ends of the spring are closed so that the end coils touch
Square (Closed) and Ground Ends (SG): the ends of the spring are closed so that the end coils touch & the end is ground to provide a flat plane

EXTENSION SPRINGS are found in garage door assemblies, vise-grip pliers, and carburetors as well as thousands of other places. When they are attached at both endsand when the components they are attached to moves apart, the spring tries to bring them together again.

Extension Springs are wound with initial tension known asstored energy which holds the coils together and offers resistance to a pulling force. Springs can have many different styles of ends, the most commontypes of loops and hooks are "Machine" and "Crossover". They can be closed (loops) or open (hooks).
Machine End: Wire comes directly off the body, then forming a circle across the center
Crossover End: Wire comes across the center of the spring
Double Loop: end consisting of two coils with no gap between the coils and the end of the wire

TORSION SPRINGS can be found on door hinges, door locks and clipboards as well as thousands of other places. When the ends of the torsion spring are attached tothe component, and when these components rotate around the center of the spring in the direction that winds the coil, the spring tries to push them back to theiroriginal position. Torsion springs offer resistance to externally applied torque as the ends are rotated in angular deflection. Commonly used over an arbor or mandrelfor support. Torsion springs are subjected to bending stress rather than torsional. Normally close wound and are left hand or right hand wound.Torsion springs are selected based on the Degree of Deflection required: usually 90, 180, 270 or 360° from the spring body.

Length of Leg: the length of the torsion spring leg is measured from the center of the body to the end of the leg or tip
Direction of Wind: torsion springs should be used in the direction that winds the coil

MBHD Carbon Steel: Medium basic carbon cold drawn spring wire per ASTM 227, suitable for parts subjected to average stress and applications; also suited to static orvery low cycles
Music Wire: Spring wire, per ASTM-228, good for parts subjected to high stresses and requiring good thermal properties. For temperatures up to 250°F
Type 302/304 Stainless Steel: Springs are manufactured to meet ASTM-A313, a high quality wire. For temperatures up to 550°F. Slightly magnetic. It is the most widelyused stainless spring wire because of high corrosion resistance properties and good tensile strength.
Black Oxide Coating (good) or Zinc Plating (better):improves the corrosion resistance of HDMB Carbon Steel and Music Wire
Passivation:an acid treatment performed on Stainless Steel Wire to remove contaminants and improve corrosion resistance
Nickel-coated Stainless Steel Springs: made from Suzuki^™ Wire^®, Nippon-Seisen wire and Sumiden® Type 302 nickel-coated stainless steel for superior corrosionresistance particularly in marine environments. Nickel plating is used in electronics because it provides a good surface for soldering, prevents tarnishing, and conductselectricity well.

Body Length: length from coil to coil, not including ends (hooks or loops)
Deflection at Load: the distance a spring compresses or extends when a given load is applied
Free Length (FL): the overall length of a spring in the unloaded position
Initial Tension (IT): the number of pounds of force it will take to overcome the tension holding the spring coils together before the spring will start to extend
Inside Dimension (ID): specified when the spring must fit over a rod or mandrel with enough clearance to operate freely
Load: the force applied to a spring that causes a deflection (i.e., movement)
Max Deflection: the difference between the overall length and maximum extension, measured on one side of spring
Maximum Extended Length: the length of an extension at full rated extension
Outside Dimension (OD):specified when the spring must fit into a circular hole ("Work in Hole Diameter) with enough clearance to operate freely or when there areother housing issues)
Pitch: the distance from center to center of the wire in adjacent active coils
Solid Height: height of a compression spring under sufficient load to bring all coils into contact with adjacent coils
Spring Rate (stiffness): the change in load per unit deflection
Stress Relieve: a process that subjects the springs to low-temperature heat treatment to relieve residual stresses
Wire Size (WD): the diameter of the actual spring wire