Observation and Measurement of Springs Using a Digital Microscope

Like screws, springs are frequently used mechanical components used in various devices such as automobiles, electrical products, and daily necessities.

This section introduces an overview on springs and introduces observation and measurement examples using a digital microscope.

Typical spring types

Coil springs

Compression coil springs
Compression coil springs generate a repulsive force when loaded in the compression direction. The structure either has an equal pitch or a taper. This type of spring is commonly used as suspension springs in automobiles.

Equal pitch coil spring

Tapered coil spring

Tension coil spring A: Hooks

Tension coil spring
A : Hooks

Tension coil springs
Tension coil springs generate a repulsive force when loaded in the extension direction. Hooks are included on both ends of the spring. This type of spring is commonly used in bicycle stands and measuring devices.

Torsion coil springs
Torsion coil springs generate a repulsive force when the coil is subjected to torsional movement around the spring’s central axis. Hooks may be included on both ends of the spring. This type of spring is commonly used in door locks and hole punches.

Torsion coil spring (with hooks)

Torsion coil spring (without hooks)

Plate springs

Flat springs
Flat springs are the most common type of plate spring and are often referred to simply as plate springs. This type of spring is commonly used in switches.

Overlapping plate springs
Overlapping plate springs are made of multiple plate springs of different lengths stacked on top of each other. The more layers that are used, the greater durability the spring will have. This type of spring is commonly used as suspension springs for trucks (also referred to as leaf springs).

Diaphragm spring

Coned disc springs
Coned disc springs are made by hollowing out the center of a conical plate spring. This type of spring is commonly used as washers to prevent screws from coming loose.

Spiral springs
Spiral springs are by winding a plate or strip of material into a spiral shape. This type of spring is commonly used in mechanical watches.

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Compression coil spring materials and dimensions

Coil spring materials

Hardened steel wire
This is the least expensive of all metal spring materials and is used in various everyday products.
Symbol : SWC
Piano wire
Offering higher tensile strength than hardened steel wire and greater hardness and fatigue resistance reliability, piano wire is commonly used for industrial springs.
Symbol : SWP
Stainless steel
Stainless steel offers better corrosion and heat resistance than piano wire, making it a mainstay of coil springs.
Symbol : SUS

Compression coil spring dimensions

Dimension description

Dimension	Description
Wire diameter	Description The diameter of the wire used for the spring. Symbol : d (mm/inch)
Average coil diameter	Description The average of the outer and inner coil diameters. Symbol : D (mm/inch)
Outer coil diameter	Description The diameter of the outer edge of the coil. Symbol : Do (mm/inch)
Inner coil diameter	Description The diameter of the inner edge of the coil. Symbol : Di (mm/inch)
Free height	Description The height of the spring with no load. Symbol : Hf (mm/inch)
Active coils	Description The number of coils used by the spring to generate force. Symbol : Na
Total number of coils	Description The number of all coils between both ends of the spring. Symbol : Nt
Pitch	Description The distance between the centers of a helically wound wire. Symbol : P (mm/inch)