These fasteners should be used when repeated access to a component is necessary. When selecting these fasteners, important factors include strength of construction, smoothness of operation, and ease of installation. Speed can be a consideration if many fasteners are involved. Simplicity of fastener design and operation can also be important. For example, a quick-release fastener with a Phillips recess offers fast access only if an operator has the required screwdriver.
Quick-operating fastener types include lever-actuated, turn-operated, slide-action, push-pull, lift-and-turn, magnetic catches, and spring-loaded devices.
Lever actuated: Draw-pull catches have a U-shaped wire bail or a flat spring-steel J-hook connected to a lever that pivots within a housing bracket mounted on one element of the closure assembly. Others have an engagement point built into a combined lever/cover that conceals all the catch assembly components in order to protect the lock and present a clean appearance.
The keeper is the element that engages the bail and is usually on the movable element of the closure assembly. These fasteners pull the two elements together tightly and lock by means of an overcenter linkage.
Some lever-actuated fasteners have coil springs or an adjustable threaded hook. These features compensate for installation inaccuracies, wear, gasket set, or damage.
The cam-actuated fastener has a cam which engages, pulls in, and locks a pin mounted in a separate keeper. The cam can be an inherent part of the lever, or it may be a separate component interconnected by a housing.
The draw-pull catch is designed for use on boxes or chests with coplanar surfaces at the parting line of lid and body. It provides moderate strength across the parting line. The spring-loaded type also has good vibration and impact resistance and requires less care to install, but costs more.
The adjustable catch tolerates greater errors at installation, permits future readjustments, and provides a solid high-strength pull down across the parting line because it has no springs. This fastener is not intended to carry loads in the planes of motion perpendicular to the parting line or along it because the lids of boxes and chests usually are fitted over mating edges. The draw-pull catch is an excellent fastener for gasket compression on container lids, hinged covers, dust-collector units, and for use on electrical control boxes where specifications will not permit fastener components to extend into the box.
Turn operated: Several types of turn-operated fasteners are available. Stud members and a retaining device, such as a nut, make up stud-type fasteners. This fastener may have multiple threads, a single fast-lead thread, or a projecting lug arrangement. They engage, compress, and hold down parts.
Pawl-type fasteners have a rotatable stud or shaft with a radially projecting pawl. The shaft is mounted through the removable panel, and the pawl engages behind the frame or supporting member. The fastener compensates for a range of material thicknesses by using a threaded shaft on which the pawl moves axially when the shaft is rotated, or it may have a fixed adjustment, in which the pawl slides along the shaft and is locked in place with a nut or setscrew. The first type provides more compressibility or pull-up and is intended for use with gaskets or where very tight lock-down is desirable. The second type operates faster.
The quarter-turn panel fastener is designed for access panels, hinged doors and plates, removable signs, large structural panels, and other applications whenever the movable (or removable) panel overlaps the supporting member, and where very rapid removal or frequent access is necessary.
Although they provide excellent ultimate tensile strength, these fasteners characteristically are spring loaded to engage and lock in a quarter turn. For this reason, they have low plate-separation load characteristics up to the distance required to fully compress the spring. If rigid, boltlike characteristics are necessary, a threaded screw fastener with fast-lead thread or an adjustable-pawl fastener should be used.
Slide action: A boltlike member is moved across the edge of the closure to engage within, or under, a keeper element mounted to the frame or body of the structure. In some cases, the keeper is not used, and the bolt directly engages the frame or panel surface. Some types are mounted entirely on the outside of the panel-frame structure.
Some slide-action fasteners are manually operated with a push, turn, or pull action. Others are spring-biased to latch when the panel closes.
The slide-action fastener converts loads on the panel to shear within the fastener and restricts motion in at least two directions. Some types have additional take-up that can be used to compress the panel tightly against a frame member or sealing gasket. The draw-pull catch is used where panel movement is along the line of engagement, while the slide-action fastener is used to resist panel movement perpendicular to it. When all components are externally mounted, this fastener also meets the requirements for control boxes.
Push-pull: This fastener usually consists of an actuating button or knob linked to a locking device on the opposite side of the panel. The locking device may engage a receiver component on the frame member, a hole in the frame member, a lip of the frame, or a shaped striker. Latching is usually accomplished by pressure engagement, pushing on either the panel or the latch button.
Variations of these fasteners are numerous, but use the following combinations of manual operations: push to lock/push to release; lock on closing/push to release; push to lock/pull to release; and pull to lock/pull to release.
Push-pull fasteners perform a basic latching function. Some play or clearance must be permitted between the attached panel and frame in the latched position, since these fasteners do not pull up or compress the panel to the frame or against a seal. Types requiring a receiver component or a hole in the frame will not tolerate much misalignment.
Push-pull fasteners are used where quick access without special tools is required and where space limitations or other factors make lift, turn, or slide action undesirable. They should be used on lightly loaded panels where the panel is not intended to be clamped against a frame or gasket.
Lift-and-turn latches: These combine lever-actuated latches and turn-operated pawl-type fasteners. A rotatable threaded shaft is used with a radially projecting pawl that can be positioned along the shaft to accommodate panel thickness. The shaft and pawl move axially when the lever is lifted or depressed, causing the pawl to move to the inner edge of a frame member. The pawl is rotated from its engagement behind the frame by rotating the lever while it is raised.
Lift-and-turn latches have the wide adjustability and compression found in turn-operated pawl-type fasteners, plus the quick action, good grip, and styling variations of lever-actuated latches.
Lift-and-turn fasteners are selected where elongated levers instead of round knobs are better suited to styling or where the better grip and mechanical advantages of levers allow tighter panel-to-frame compression. They are chosen for compression or sealing applications where quick operation is desirable and because the lever position allows a quick visual check on the status of an application where a number of such latches are used together.
Such latches are available with raised handles or with "flush" handles that lie close to the panel. Flush latches are operated by pushing in at one end of the lever, grasping the other end, and turning. Keylock styles are also available.
Magnetic catches: A magnetic catch consists of a magnetic core piece sandwiched between the two steel pole pieces. The magnet and its pole pieces are contained in a plastic or nonferrous housing that also provides a way to install or attach the catch. A small flat steel plate or "armature" is also provided and is installed on the mating component of the closure. The holding force does not usually exceed 15 lb, and 4 to 10 lb is very common.
Magnetic catches provide quick access where the forces required to keep the door closed are low, and a positive mechanical door-to-frame connection is not required for safety. The outer door or panel surface does not need to show any evidence of fastener attachment, and if an edge is accessible to pull upon, no other knob or finger hold is needed.
Magnetic catches have no moving parts to wear out, and are usually reliable, trouble free, and little affected by normal environments. The only maintenance required is to occasionally wipe off the contacting surfaces. Installation is quick and economical.
Spring-loaded devices: Spring-loaded plungers provide end forces for purposes of detent or holding parts in place. The body of such a plunger looks like a threaded insert, and plunger bodies come in a variety of thread sizes and with various locking devices, as do inserts. However, the body contains a spring and a plunger or ball.
The spring force, which may range from a few ounces to tens of pounds, is transmitted to the plunger or ball. The plunger or ball presses against a flat surface on the mating part, or into an indentation or hole which provides further locking action.
Plungers are available with various lengths of travel, and end force increases as the plunger is depressed. Ball plungers have very little travel, and provide a rolling action instead.
Advantages of spring-loaded plungers include quick operation and variable positioning. Such devices are available in a variety of materials for standard and special purposes, such as for use as electrical contacts.