What are the parts of a hinge?
While there are many different types of hinges, most still share the same basic parts. It’s these hinge parts that we’re going to explain, which will help you better understand how hinges work. We’ll cover these parts of a hinge:
Leaf
The leaf is the flat, extended part that attaches to the surface of the object – typically a door or cabinet – and provides support for the rest of the hinge parts. Usually made of plastic or metal, these parts of a hinge are essentially moving plates that rotate with the object they’re connected to.
The size and shape of the leaf can vary. It depends on the size and weight of the object it supports. Different types of hinges may have different configurations of leaves and other hinge parts, such as the strap hinge shown here. Each leaf is designed to provide maximum support and stability for the heavy weight of the door it’s attached to.
A hinge leaf may be wider or longer to provide more support for a heavy door or cabinet. Other hinges have a single leaf, such as the unique butt hinge shown here, used for HVAC systems, electrical panels and machinery panels. Heavy-duty free-swinging hinges are ideal for large flush-fitting doors. Installation is easy and enables quick access to carry out maintenance or make repairs.
You can learn more in our guide Different hinge types and where to use them.
Knuckle
A knuckle is also called a node or loop. This is a cylindrical or conical shape located at the point where the leaves meet and is often the thickest part of the hinge. In the illustration above, we see five knuckles. These knuckles together form what’s called the barrel. Knuckles are actually not parts of a hinge. That is, they form when the leaf is joined together.
The knuckles connect the leaves and allow them to pivot around the pin. They can be thought of as the "hinge joint" that provides stability and strength to the overall hinge structure. The size and shape of the knuckle can vary depending on the type and design of the hinge.
Note the offset hinge shown here and its singular knuckle. The design enables a door to be opened so that it gives you a clear, unobstructed path. Without this type of hinge, the doorway would have to be larger. Hospital doors are a good example of where this hinge is used.
This piano hinge is also called a continuous hinge. Note the continuous line of knuckles. A continuous hinge is ideal for applications that are constantly being opened and closed, and subject to intense wear and tear.
You can learn more in our Guide to piano hinges.
The knuckle plays a critical role in the function of a hinge, as it provides the necessary support and stability for the leaves to rotate around the pin. It also helps to distribute the weight and stress of the door or object that the hinge is attached to, which helps to prevent damage or failure of the hinge over time.
Pins
The pin, also called a pintle, is a cylindrical rod or shaft that runs through the knuckles of a hinge, connecting the two leaves and allowing them to pivot around it. It is typically made of steel or another strong metal and is precisely machined to fit snugly into the knuckles of the hinge.
The pin provides the necessary pivot point around which the leaves rotate. As the door or object that the hinge is attached to is opened and closed, the pin moves within the knuckles, allowing the leaves to pivot smoothly and without friction.
The material used to make the pin is important, as it must be strong enough to support the weight of the door or object that the hinge is attached to. This side hinge has a stainless steel pin, as it’s strong, durable, and resistant to wear and corrosion. It’s ideal for heavy doors. A side hinge with a pin made of zinc alloy would be suitable for machinery covers.
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