A metal hitch lock is a device used to join two objects together. It can consist of a range of different materials, from steel and aluminum to bronze or copper. These devices can be as simple as metal sleeves used specifically to join two or more pieces of fabric, or as complex as a mishap found in a wagon or construction equipment. Different types of couplers are also known as couplings, and must be chosen based on their actual size, strength and proposed function to ensure that they will meet the demands of each project.

The simplest units use a simple compression metal coupler or even have a clamp design. Once they are in the right place, force is applied to the outside of the coupler, which causes it to grab the object at the bottom using resistance to compression. The bar is similar to the beam design of the metal coupler that can be used to join two internal shafts on small machines. Some of these couplers have a beam style that uses a screw-like mechanism instead of compressing them to keep them in place. This type of design has a beam or bar that is only suitable for relatively simple applications that require minimal holding force.

For example, wagons and heavy equipment often rely on a heavy metal coupler to join multiple cars or units. Classic wagons rely on a hook and pin coupler made of heavy iron, or a hook that connects to a series of links in a steel or iron chain. These couplings were used to allow workers to connect and disconnect wagons relatively easily. This type of metal coupling is still widely used today in modern construction equipment. Another example of this are cranes that can incorporate a hook and a pin-style coupler for quick attachment and good detachment by parts of the work teams. They have the same principles as a ball and their design features a quick coupling with other couplers.

More complex applications require complex metal designs. These advanced models often allow one or both components to be able to move once they are connected. An example of this is the gear or disc coupler, which joins two components together using a series of locking teeth and a protective metal sleeve. Bellows joints are similar, and consist of an accordion-style design that allows the joint to flex and move during the transfer of movement between the two objects. Even a chain and pinion can be considered a type of metal hitch. In this model, a metal chain connected to an axle or motor could join with a sprocket connected to a separate shaft or motor, and transfer impulse or energy between the two.