An anchor shackle is a type of U- or O-shaped metal piece used to secure a moving object to a stationary one. It has a gate for closure and can be bolted or pinned shut, or spring-loaded. The rounder the shackle, the better it balances forces on it.
A shackle is a U- or O-shaped piece of metal attached with a bolt, pin, or spring that connects the elements together. An anchor shackle is a specific type of shackle that is used to secure a moving object to a stationary object. The shape of the anchor shackle allows the moving object to push and pull from different directions without creating a shear force on the device. These shackles have many industrial uses, but are especially common on boats. There they do everything from holding lines to setting the boat’s actual anchor.
Load-wise, a shackle is a solid metal ring. To be a real shackle, there cannot be any openings in the ring that makes up the fastener. Since the shackle would be of little use if it were simply a solid ring of material, it has an opening called a gate which can be closed. There are several methods used to close the gate in the shackle in order to effectively create one piece.
There are two common fastening methods for most shackle bolts or pins. For these shackles, the bolt or pin forms part of the ring itself. When they are open, the bolt or pin that holds them closed is typically removed completely from the shackle. When in use, a bolt-on shackle has a set of threaded rings on each side of the opening that allow the bolt to hold the shackle closed. A pin shackle is very similar, but the pin simply slides through the opening and is secured on both sides.
Spring loaded shackles have a spring or tension system that allows the user to open the shackle without removing the connecting piece. The gate opens by pressing on the shackle; in this way a load cannot accidentally push the gate outwards. While both bolt and pin systems are commonly used to secure an anchor shackle, spring loaded systems are not.
Anchor shackles attach to a stationary and a moving object. The gate on the shackle generally faces the stationary object and the majority of the shackle faces the moving one. An anchor shackle is usually round; the rounder the shackle, the better it balances the forces on it. The round shape allows the moving load to pull from any direction, yet still have the same relative force applied to the anchor shackle. A round shackle is generally lighter than a U-shaped shackle of the same weight, but can withstand changes in directional force that would damage the U-shaped version.
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