A fifth wheel is a part that almost anyone in industrial trucking is familiar with. We know it works to connect the semi truck tractor and trailer, and if you’ve been in the business for a while, you might even be familiar with a few of the key features that are nice to have in top-of-the-line models.

But when there are so many options to choose from on the market today, it can be helpful to know what you truly need to have and what options are add-ons. Since all fifth wheels are manufactured a little differently, we’re going to dive into the 5 essential parts of a fifth wheel. This should give you the information you need to find the best fifth wheel for your unique application.

01. Top Plate


The top plate is the cast part of the fifth wheel. It usually looks like a large horseshoe shape. The top plate secures coupling components and vertical trailer or cargo load. It’s the largest component of a fifth wheel.

02. Release Handle


Not all fifth wheels have this type of handle — the release handle (shown blue in the image above) is a unique part specific to JOST fifth wheels. In a JOST fifth wheel, the release handle makes it easy for operators to couple and uncouple a fifth wheel while ensuring ultimate safety.

The release handle also provides operators with secondary locks and visually indicates that the coupling is secure. While not all fifth wheels feature a release handle, JOST has prioritized this part for the safety and security of all our customers. When operators can visually confirm that tractor-trailer coupling is successful, there’s no guesswork, and you know you’re hauling safely.

03. Lever


The lever is a relatively small component of a fifth wheel, but that does not make it unessential. The lever links the release handle to the locking bar. Together, all three components work to slide the locking bar across the opening of the cushion ring, supporting and securing the lock jaw and ensuring the tractor and trailer are appropriately coupled for transit.

04. Lock Jaw


The lock jaw is the coupling mechanism that locks around the kingpin to hold it in place. In the above image, you can identify the lock jaw by it’s “C” shape. This shape allows the jaw to fit snugly around the kingpin. It is connected to the lever and release handle, and is the primary securing mechanism holding the tractor and trailer together.

05. Lock Bar

locking bar

A fifth wheel’s lock bar secures the lock jaw. When engaged, the lock bar slides across the opening of the cushion ring, under the lock jaw, and ensures the trailer kingpin is held firmly in the fifth wheel and is secure for transit. The lock bar provides superior structure to support trailer drawbar load.

Are these the only components of a fifth wheel?

While these five components are essential to the safe functionality of any fifth wheel, they are not the only components. For example, JOST fifth wheels also offer a range of features to ease operation and extend product life cycle, including:

adjustment screw
  • Adjusting Screw. This allows the locking bar to maintain a snug coupling even as the lock jaw and cushion ring wear.
  • Grease Fitting. This delivers grease directly to the kingpin and lock jaw contact point to ensure that all parts are properly lubricated to extend the life of both products.
  • Cushion Ring Insert. This works to protect the kingpin and top plate casting from wear and damage.

There are a number of additional components featured on JOST fifth wheels, but the five mentioned above are essential to the functionality of every fifth wheel. At its core, a fifth wheel must have:

  • A top plate for the trailer to rest on
  • A securing mechanism to hold and secure the kingpin
  • An operational mechanism that allows the driver to couple and uncouple tractor and trailer

With a better understanding of each of these components and their importance to the safety of your daily operations, you’ll be able to select the ideal fifth wheel product for your specific application’s requirements.

If safety and durability are priorities for your fleet, JOST fifth wheel products deliver. Check out our parts online, or get in touch with our team to find a dealer near you.