FAQs and Terminology
Terminology Common to All Springs
Active Coils – The coils which are free to deflect when the spring is loaded.
Total Coils – All coils including the end coils.
Counting Coils – Look at the end of the spring, turn the spring the wire is at 12.00 o’clock, follow the wire round, each time the wire passes 12.00 o’clock it is a complete coil, when reaching the last full coil stop and estimate the remaining wire ie, ¼, ½ or ¾ etc. then add this to the number of full coils.
Spring Hand – The direction in which the spring is wound, Right or Left Hand.
Right of Left Hand – Look at the end of the spring, turn the spring so the start of the wire is at 12.00 o’clock, if the direction of the wire is to the right the spring is Right Hand (R/H), if the direction of the wire is to the left the spring is Left Hand (L/H).
Mean Coil Diameter – Outside spring diameter (O/D) less one wire diameter.
Deflection – Movement of ends of spring when a load is applied.
Rate – Change in load per unit deflection, normally given as pounds per inch (lbs/in) or Newton’s per millimetre (N/mm).
Load – Pressure at a given deflection.
Terminology Specific to Compression Springs
Free Length – The overall length of a spring in the unloaded position.
Pitch – The centre of wire to the centre of wire of adjacent active coils (best practice is to specify active or total coils).
Ends Closed – Where the end of spring pitch is reduced so the end coils touch.
Closed and Ground Ends – As Ends Closed but ground square for more stable location.
Solid Height – Compressed length of a spring, when all the coils are touching with no spaces between.
Terminology Specific to Tension Springs
Pull to Pull – The measurement between inside the wire hooks/loops at the end of the tension spring.
Hooks – Cut loops to form a hook for attaching spring to location.
Loops – Spring end coils lifted up from body of spring to form full loops for attaching spring to location.
Initial Tension – The pressure that keeps the coils of an extension spring together and must be overcome before the coils will open.
Terminology Specific to Torsion Springs
Free Angle – Angle between the legs of a Torsion Spring when there is no load applied.
Torque – A twisting action in torsion springs which produces rotation, equal to the load multiplied by the distance (or moment arm) from the load to the axis of the spring body.