Most domestic window and door screens typically ‘snap’ back to their original closed position once you let them go, and a significant proportion of them do so through the use of extension springs.

In most setups, the tensioned springs are attached at one end to the side of the window screen, and at the other to a non-moving window track or door frame.

When a pulling force is transferred through the extension spring by somebody opening the screen, the spring itself will typically extend outward and attempt to pull the screen back into its original position. When closed, the spring returns to its original tightly wound shape and holds the screen closed.

Tension springs for door and window screens are generally positioned above or to the side of the screen itself, such that no additional space allowance is needed for fitting them, making them a quick and easy addition to almost any door or window hardware kit.

Garage doors - particularly sectional or rollover types - very often work with extension springs to help the heavy door open and close more smoothly, with less support and/or lifting force required from the operator.

One end of the tension spring is generally attached to a fixed bracket above the door, while the other end will be affixed to the door itself, each via a pulley mechanism. The tension in the spring counterbalances the weight of the garage door as it moves downward into position, attempting to pull it back up and thus stopping it from falling into place too quickly or heavily.

When the door is fully closed, the spring will therefore be at full stretch. When it’s time to open the door again, the extension spring trying to contract again helps lift the weight of the door back into position, making the job much easier for the operator. Once the garage door is fully open, the extension springs above it will have returned to their least stretched position, and the majority of the door’s weight will be supported by the runner tracks it slides onto.

It’s very common for electric guitars to offer a vibrato or tremolo action, which allows the player to vary the pitch of a note quickly by applying downward force to a lever arm on the body of the instrument.

This lever is connected to the guitar’s bridge via a series of slim tension springs, which are set up such that they attempt to pull the bridge back to its original position when the player applies force to the tremolo arm. The tension on these springs must be balanced against the tension and gauge of the guitar’s strings, which continually attempt to pull the bridge of the instrument in the opposite direction.

In order for a stable tuning to be achieved, these two opposing forces must be in equilibrium - this will allow the bridge of the guitar to lie perfectly flat against the body of the instrument. Most guitars therefore offer multiple points of adjustment for each source of opposing tension, from the machine heads at the ends of the strings to the screws holding the claw attachments for the extension springs.

Pool cover tension springs work much like they do on a trampoline - in other words, the springs positioned around the edge of the swimming pool safety cover can be stretched inward, allowing the cover to be pushed down some distance while attempting to drag it back into position.

Unlike a trampoline, they’re not tensioned to provide excessive bounce, but rather to allow for additional weight to be applied on top of the pool cover - either due to pool water ingress, precipitation, or objects/people falling onto it - without the cover or its support straps immediately breaking or sinking beneath the surface.

Pool cover extension springs are generally anchored directly into the ground or brickwork surrounding the water at one end, and attached to the cover via s-hooks passed through loops at the other.

Sofa beds and other sorts of fold-out furniture - certain spring-loaded tables or fold-away surfaces, for example - very often feature extension springs to help support heavier sections and make the job of setting them up and putting them away again much easier for the user.

In a typical fold-out sofa bed setup, the tension springs work much as they do for a garage door: as the sofa bed is fully opened out, the spring will near its full stretch position, attempting to pull the open section of the bed back into a folded configuration.

To ensure that this doesn’t happen until deliberately moved, most sofa bed springs will be arranged with a series of springs providing pulling forces in different directions. This allows a second tension spring to assume a majority of the supporting role once the fold-out sections move beyond a certain point in their arc.

Extension springs for upholstery - especially common on to many types of armchairs and settees - again work much as they do for a trampoline.

One end of the tension spring is attached to the base of the seat, while the other is affixed to the non-moving frame of the sofa or chair itself, allowing the seat to depress under the weight of the sitter before returning it to its original position once the force is removed.

As well as offering far more comfort for the sitter, this also helps to prolong the useful life of the furniture, reducing overall wear and strain on fixed parts of the frame. Because tension springs are generally cheap to replace and fairly quick and easy to fit, they can be swapped out multiple times to keep the same sofa or armchair feeling comfortable and cushioned even over very long periods of daily use.

• Stock extension springs are the ‘basic’ version of the classic extension spring design outlined at the start of this guide.
• Generally speaking, they’ll feature a series of helical steel coils wound tightly together, with a hook or loop at either end for easy attachment to other components as part of a load-bearing and force transferral mechanism.

• Precision tension springs are generally manufactured under particularly tight tolerances, and from especially high quality materials, in order for the resulting product to be more exact in terms of its physical dimensions and the forces it’s designed to support.
• In certain dynamic or heavy cycle applications, such as maintenance, prototyping or equipment repair, fitting precision extension springs can significantly extend the life of key equipment and mechanisms before replacement is needed.

• Certain manufacturers and suppliers allow for precise sizes, steel gauges, load requirements and material/coatings of extension springs to be specified by the customer on ordering.
• This can be useful in certain highly specific applications where more standard configurations won’t work due to space constraints or especially demanding environments.

• Safety drawbar springs are effectively a combination of extension and compression spring in a single piece of hardware.
• They feature a special assembly that, when a load is applied, allows the main spring to compress as the drawbar extends, while simultaneously providing a fixed stopping point that prevents overstretching (hyperextension).
• In the event of a complete failure and breakage of the spring, the drawbar feature also takes over load-bearing duties, meaning certain types of otherwise potentially hazardous equipment - such as suspended seats, platforms and doors - remain supported until the assembly can be replaced.

• Extension springs for heavy duty uses typically come in thicker steel widths, often have wider overall diameters, and will be able to support considerably higher load forces than standard smaller gauge tension springs.
• This is important for many industrial extension springs commonly used in mechanical applications where a great deal of pulling force needs to be applied safely, such as is often required in heavy machinery components for the agricultural, petrochemical and automotive sectors.

• Most extension springs are sold either with hook or loop ends, each of which offer different types of anchoring points and can be more convenient to attach to particular sorts of hardware and equipment.
• Hook ends, usually provided in the form of an s-hook, are generally the easiest type to quickly attach and reattach to various items; loop ends require more work to attach, but can usually provide more robust anchoring once installed (since the loop has no break in it to provide a potential fail point during hyperextension).
• Both extension springs with hook ends and loop ends can be configured as crossover, machine style or side style - the best and most cost-effective choice will generally depend on the intended application, and how much force you’ll need the spring to support.