On this page, we have attempted to give you a short explanation of the terminology that is used to describe our springs and washers, their technical characteristics and their features. For most of our main product lines, we have also developed a series of FAQs for answers to the most common questions in the spring industry.
Compression Springs | Extension Springs | Torsion Springs | Belleville Washers | Wave Washers | Curved Washers | Finger Washers
We have also covered frequently asked questions for our Gas and Mechanical Struts:
Struts - Frequently Asked Questions
Tolerances Info is for guide purposes, for more detailed specifications please refer to our catalogue and/or contact us.
O.D. (Outside Diameter):
I.D. (Inside Diameter): For springs manufactured to O.D., the I.D. can be computed by subtracting 2 wire diameters ("d") from the O.D. It should be understood that this will provide an approximate value. For applications requiring the spring to fit over a shaft, 2.5 wire diameters should be subtracted from the O.D. to approximate the I.D.
d (Wire Diameter): Normally, wire diameter is as specified. Tolerances are as per the material specifications to which it is purchased. Distortion during coiling changes the wire diameter slightly, and indicated diameter is always prior to forming. It is suggested that tolerances for drawings be ± 0.025mm of the published value.
LØ (Free Length): The free length is an approximate dimension. It should be understood that all springs have a built-in free length tolerance resulting from the O.D, wire, load and rate being toleranced.
P (Load P): The description lists the load for each spring. As published, all loads have a tolerance of ±10%. The load should be measured by deflecting the spring to the length L1 specified. For stainless steel, the load should be multiplied by 0.833.
L1 (Length): Is the length to which the spring should be compressed to measure the load P. It is a fixed value. L1 is also the maximum compressed height before set.
R (Spring Rate): The description lists the rate for each spring. As published, all rates have a tolerance of ± 10%. The rate should be checked at load heights corresponding to 25% of P at L1. For stainless steel, the rate should be multiplied by 0.833.
Solid Height: The description lists the approximate solid height for each spring. It is important to note that this dimension is always approximate because it is based upon theoretical coil numbers. We do not recommend that springs be operated near solid height due to inaccurate loads resulting from the non-linearity of the spring rate near solid height.
FAQs
Number of coils: It is always a reference dimension.
What about the grind? All springs with exception of the C0057 and C0058 series and wire diameters below 1mm are ground on both ends. The grind is a minimum of 270°.
And the squareness? Squareness is within 3° for the springs in the free position.
Helix? All compression springs are right-hand wound.
What is the finish? The finish is that of the plain wire. Music wire is oiled to prevent corrosion.
Is the spring magnetic? Stainless steel is slightly magnetic.
What is the linearity? Compression springs are linear between 15% and 85% of the spring's available travel. Available travel can be computed by subtracting the free length from the solid height.
Has the set been removed? Set has not been removed from our stock springs. Deflecting a spring past L1 will cause it to take set. Set can be removed by compressing the spring to solid height. Most of the set will be removed after one compression. Excessive loads at solid height should be avoided, since they could distort the spring permanently.
Can it deflect past L1? Yes. However, it must be realized that the spring may set slightly.
Can the spring buckle? As a rule of thumb, buckling can happen when the free length (L) is = 4 times the O.D.
Tolerances Info is for guide purposes, for more detailed specifications please refer to our catalogue and/or contact us
O.D. (Outside Diameter):
d (Wire Diameter): Normally, wire diameter is as specified. Tolerances are as per the material specifications to which it is purchased. Distortion during coiling changes the wire diameter slightly, and indicated diameter is always prior to forming. It is suggested that tolerances for drawings be ± 0.025mm of the published value.
LØ (Free Length): The free length is an approximate dimension. It should be understood that all springs have a built-in free length tolerance resulting from the O.D., wire, load and rate being toleranced.
P (Load P): The description lists the load for each spring. As published, all loads have a tolerance of 10%. The load should be measured by deflecting the spring to the length L1 specified. For stainless steel, the load should be multiplied by 0.833.
T (Initial Tension): The initial tension is the force required to slightly separate the coils. This dimension is approximate.
L1 (Length): Is the length to which the spring should be extended to measure the load P. It is a fixed value. L1 is also the maximum extension for static applications.
R (Spring Rate): The description lists the rate for each spring. As published, all rates have a tolerance of ± 10%. For stainless steel, the rate should be multiplied by 0.833.
FAQs
Number of coils: It is always a reference dimension.
Helix? Extension springs are left- or right-hand wound.
What are the hooks? All extension springs have full hooks which have not been cut for installation purposes. Closed loops are provided to help alleviate tangling. The I.D. of the hook is approximately equal to the I.D. of the spring body.
What is the finish? The finish is that of the plain wire. Music wire is oiled to prevent corrosion.
Is the spring magnetic? Stainless steel is slightly magnetic.
Can it be deflected past L1? No. L1 is the recommended maximum deflection for static applications.
And for the dynamic applications? For dynamic applications (2,000+ cycles) the customer should apply a maximum load of approximately 75% of the catalogue load P. We recommend pre-loading the spring to prevent surging.
Tolerances
O.D. (Outside Diameter): The description lists the O.D. for each spring. All have a tolerance of ±5%.
I.D. (Inside Diameter): For springs manufactured to O.D., the I.D. can be computed by subtracting 2 wire diameters ("d") from the O.D.
d (Wire Diameter): Normally, wire diameter is as. Tolerances are as per the material specifications to which it is purchased. Distortion during coiling changes the wire diameter slightly. It is suggested that tolerances for drawings be ± 0.025mm of the published value.
Position of Legs: There are 4 leg positions. Each is shown on the torsion spring description. The initial leg position is represented using solid lines, and the final position is represented using dashed lines. The listed torque "M" is measured at the final position.
Deflected Degrees: This is the maximum deflection for all springs. Springs deflected more may take a set. It should be noted that all springs should be deflected in the direction which will wind the spring. Unwinding the spring will cause premature set, and is not recommended.
M (Torque): The torque values for all springs can be found in the description, and are given as reference only.
R (Radius): The radius is the point at which the load is applied to check the torque at manufacturing. It is measured from the centre axis of the spring. In all cases the radius is 0.5 of the leg length "E". Radius is not 0.5 of the O.D.
Suggested Mandrel: This is the maximum suggested mandrel size which should be inserted through the spring I.D. The mandrel is smaller than the spring I.D. to allow for sufficient clearance when the spring is fully deflected. Too large of a mandrel may cause binding and/or distortion.
E (Leg Length): It is the distance from the centre axis of the coil body to the end of the leg. See description for values.
Minimum Axial Space: Recommended space along shaft for the spring under full deflection. The published values provide clearance for the spring to prevent binding. The axial space does not indicate the width of the coil body.
FAQs
What is Torque? Torque is the product of a force multiplied by a distance. It is measured in N/mm. Torque should not be confused with Load.
What position is Torque measured at? The Torque "M" listed in the description is at the maximum deflection. Since the torque is linear, intermediate torques can be computed by proportion. For example: if a spring is deflected 0.5 of the maximum value, the torque is 0.5 of that printed value.
Does the Load change? The load on a torsion spring can vary for the same torque and deflection depending upon the position on the leg where the force is applied. The load decreases as the point of contact moves out from the centre axis of the spring. If a specific application extends the length of the spring leg, i.e. lever, the lever must be considered as an extension of the leg of the spring.
What is the Helix Direction? A right-hand-wound spring loads in a counter-clockwise direction. A left-hand-wound spring loads in a clockwise direction. Both are available.
Tolerances Info is for guide purposes, for more detailed specifications please refer to our catalogue and/or contact us
O.D. (Outside Diameter): Washers are designed to fit into hole as shown in the description. Therefore, the O.D. values are less than the listed maximums. This allows for sufficient clearance when the washer is deflected.
I.D. (Inside Diameter): Washers are designed to fit over a rod as shown in the description. Therefore, the I.D. values are greater than the listed minimums. This allows for sufficient clearance when the washer is deflected.
H The overall height "H" is an approximate value. It is slightly adjusted around the published value at manufacturing to meet the load "P1" at the deflected Height "H1". It should be noted that the height is the only variable that is adjustable in the manufacturing process due to the O.D., I.D. and material thickness being fixed.
P1 (Load P1): The description lists ranges for the load which can be expected when the washer is deflected to the height "H1". The loads are based upon a process capability index of 1.33 Cpk. Note: When load-testing Belleville washers, it is imperative that extremely accurate height measurements be taken. Accuracy should be to 0.0025mm
P flat (Load at flat): This is the theoretical load at flat used for design purposes. Load testing at flat is inaccurate due to the inability for exact height measurements at the flat position. Also, when nearing flat, Belleville washers tend to experience a change in contact points. This change results in an increase in load over the theoretical near-flat.
H1 (Deflected Height): This is the height to which the washer should be compressed to measure the load "P1".
FAQs
Can it deflect past H1? Yes. The loads listed in the catalogue are generally at a 50% deflection. It should be noted that loads are greater than computed when a washer is deflected more than 75% of its available travel.
Is the spring magnetic? Stainless steel is slightly magnetic.
What kind of plating? Electroplating is not recommended due to the possibility of the washers breaking due to Hydrogen cracking. Mechanical plating should be used because it substantially reduces this risk. The washers can also be black oxided, or phosphate coated.
What are the advantages of Series stacking? Series stacking increases the amount of available travel. The load-carrying ability of the stack does not increase. In a theoretical world, the applied load is equally transmitted to each washer.
What are the advantages of parallel stacking? Parallel stacking increases the load proportionally to the number of washers.
What is the finish? It is that of the plain material. Carbon steel is oiled to prevent corrosion.
Tolerances Info is for guide purposes, for more detailed specifications please refer to our catalogue and/or contact us
O.D. (Outside Diameter "A"): The values shown in the description are those of the blank size before bending. The formed washers become ovate during forming.
I.D. (Inside Diameter "B"): The values shown in the description are those of the blank size before bending. The formed washers become ovate during bending.
H: The overall height "H" is an approximate value. It is slightly adjusted around the published value at manufacturing to meet the load at the deflected Height "H1". It should be noted that the height is the only variable that is adjustable in the manufacturing process due to the O.D., I.D. and material thickness being fixed.
Load (Load at H1): The description lists ranges for the load which can be expected when the washer is deflected to the height "H1". The loads are based on a process capability index of 1.33Cpk.
H1 (Deflected Height): This is the height at which the washer should be compressed to measure the load.
FAQs
Can it deflect past H1? Yes. It should be noted that loads are greater than computed when a washer is deflected more than 80% of its available travel. It must be understood that the spring may set, however.
What is the linearity? Wave washers are linear between 20 and 80% of the spring's available travel. Available travel can be computed by subtracting the thickness "t" from the height "H".
What kind of plating? Electroplating is permitted although Hydrogen cracking is still possible. Mechanical plating can be used as an alternative because it substantially reduces this risk. The washers can also be black-oxided, or phosphate-coated.
What are the advantages of parallel stacking? Although Parallel stacking increases the load proportionally to the number of washers, it is not recommended, due to the manner in which wave washers orientate in parallel.
Is the spring magnetic? Type 302 stainless steel is slightly magnetic.
What is the finish? It is that of the plain material. Carbon steel is oiled to prevent corrosion.
Tolerances Info is for guide purposes, for more detailed specifications please refer to our catalogue and/or contact us
O.D. (Outside Diameter): Washers are designed to fit into hole as published in the description. Therefore, the O.D. values are less than the listed maximums. This allows for sufficient clearance when the washer is deflected.
I.D. (Inside Diameter): Washers are designed to fit over a rod as published in the description. Therefore, the I.D. values are greater than the listed minimums. This allows for sufficient clearance when the washer is deflected.
H: The overall height "H" is an approximate value. It is slightly adjusted around the published value at manufacturing to meet the load at the deflected Height "H1". It should be noted that the height is the only variable that is adjustable in the manufacturing process due to the O.D., I.D. and material thickness being fixed.
Load (Load at H1): The catalogue lists the nominal load which can be expected when the washer is deflected to the height "H1". The loads are based on a process capability index of 1.33Cpk.
H1 (Deflected Height): This is the height at which the washer should be compressed to measure the load.
FAQs
Can it deflect past H1? Yes. It should be noted that loads are greater than computed when a washer is deflected more than 80% of its available travel.
What is the linearity? Curved washers are linear between 10 and 80% of the spring's available travel. Available travel can be computed by subtracting the thickness "t" from the height "H".
Is the spring magnetic? Stainless steel is slightly magnetic.
What kind of plating? Electroplating is not recommended due to the possibility of the washers breaking due to Hydrogen cracking. Mechanical plating should be used because it substantially reduces this risk. The washers can also be black oxided, or phosphate coated.
What are the advantages of Parallel stacking? Parallel stacking increases the load proportionally to the number of washers. It should be noted that curved washers in parallel could misalign causing erratic loads.
What is the finish? It is that of the plain material. Carbon steel is oiled to prevent corrosion.
Tolerances Info is for guide purposes, for more detailed specifications please refer to our catalogue and/or contact us
H (Overall Height): is an approximate value.
Load: The catalogue lists ranges for the load which can be expected when the washer is deflect to a height of 1.57mm The loads are based upon a process capability index of 1.33Cpk.
Gas Struts should be mounted so that the rod points down in the inactive state. This ensures that the internal guide and sealing system remains lubricated.
Ball joints are best in avoiding side load forces. Such forces may lead to premature failure. If eye or clevises are to be used, ensure a clearance fit to allow lateral movement.
Consider fitting a Varilift Gas Strut in order to find the correct working force. We will measure this and supply custom fixed force gas struts. Alternatively, complete the Engineering Worksheet (see Request a Quote section) and we will calculate it for you.
Standard sizes are available in any pressure within the minimum and maximum for the range. Custom sizes are also available, but may be subject to increased lead-time.
Physically limiting the extremes of the operating stroke will prevent damage occurring through excessive loading. Compression type struts should never be used to limit opening or other movement.
Our gas struts are designed to operate between -30° C and +80° C.
Our mechanical struts are designed to operate up to 300° C
Gas Struts are maintenance free. They do not require greasing or lubrication.
Long periods between operation may result in loss of pressure or damage through dirt build up.
For this kind of application we recommend the mechanical strut.
If storage is required, gas struts should be stored with the rod pointing down. Avoid the use of adhesive tapes, which may leave residue and result in damage to the seals.
Do not attempt to dismantle the gas strut or refill with gas. This is a hazardous process. Contact us regarding your application, as an alternative mechanical solution may be possible.
Gas struts should be disposed of in an environmentally correct manner. Do not puncture or incinerate.
Associated Spring SPEC Ltd.
T: 01386 443 366 E: sales@assocspring.co.uk
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