How to Choose the Best 5th Wheel Pin Box for Your Rig

While most 5th wheel trailers come with a pin box already installed from the factory, there comes a time when replacing or upgrading your 5th wheel pin box is necessary.

In this guide, we’ll walk through how to choose the best 5th wheel pin box for your 5th wheel trailer. Our goal is for you to come away from this guide feeling confident and ready to make an informed decision that fits your lifestyle, existing equipment, preferences, and budget.

Here’s what we’ll cover:

• What is a pin box anyway?
• What are some types of pin boxes?
• What shock-absorbing options are there?
• What’s important when searching for the right pin box?

Let’s start off by clearing up any confusion around the parts of a 5th wheel connection. There are three essential components that make up the immediate 5th wheel trailer coupling point.

A 5th wheel pin box is the tongue or coupler on a 5th wheel trailer that allows it to hitch up to your truck. The pin box is mounted on the front, upper deck of the trailer, protruding from the underside of the trailer overhang.

There are many different types of pin boxes, from basic units to advanced models with shock-absorbing features. Most pin boxes are adjustable to accommodate different truck-trailer setups.

A 5th wheel king pin is sometimes confused with the pin box we’ve just mentioned. However, the king pin is only one part of the complete pin box.

The king pin is the immediate connection point between the pin box on the trailer and the 5th wheel hitch in the truck bed. It is a cylindrical piece of metal that allows the connection to swivel freely within the hitch jaws, enabling the truck and trailer to turn smoothly.

A 5th wheel hitch is a type of trailer hitch that mounts in the bed of a pickup truck and provides a coupling point for the pin box of a 5th wheel trailer. The hitch mimics the design of a semi-truck hitch, featuring a large, flat head with open-close jaws to close around the king pin.

5th wheel hitches come in all shapes and sizes to accommodate different truck and trailer sizes and various budgets.

To learn more, check out our complete guide to 5th wheel hitches.

A fixed pin box is a basic model that is comprised of the pin box body, mounting brackets, and a king pin. It is called “fixed” because, once installed, the parts are not designed to pivot or hinge in any way.

It should be noted that, while fixed pin boxes don’t have articulating components, most are designed for some level of adjustability. The mounting brackets often come with multiple mounting holes to allow the pin box to be adjusted up or down on the nose of the trailer.

A rotating pin box or turret-style is engineered for short-bed trucks. While most pin boxes place the pivoting point on-center with the king pin, a rotating box positions it back where the box bolts onto the trailer frame. Having this rearward displacement allows for increased truck-trailer clearance and enables the setup to complete tighter turns without obstruction.

Rotating 5th wheel pin boxes do require a wedge or other solution at the king-pin-hitch connection to anchor the rotation of the original coupling point. In other words, the connection cannot have two pivot points, so one of them must be stopped and made rigid.

A gooseneck 5th wheel pin box is an adapter-type pin box. It is designed to mount onto a 5th wheel trailer frame, but instead of providing a king pin to connect to a 5th wheel hitch, it provides a gooseneck coupler to connect to a gooseneck hitch.

Gooseneck hitches are sometimes preferred for their low-profile, unobtrusive design and lightweight approach to the towing components (i.e. a simple trailer ball and two safety chain anchors). They’re popular among agricultural and commercial settings, and they can be used to tow a 5th wheel trailer with the right gooseneck pin box installed.

Shock-absorbing 5th wheel pin boxes (a.k.a. pivoting pin boxes or cushion pin boxes) are all about enhancing ride quality and comfort. 5th wheel trailers are heavy, and towing them can create all kinds of vibrations, chucking, and noise at the coupling point. This also means they can subject your truck and equipment to increased wear and tear. Shock-absorbing pin boxes aim to reduce these effects.

There are many different methodologies to shock-absorption within 5th wheel towing alone. This results in many different options of shock-absorbing pin boxes. Some use pivoting mechanisms with integrated rubber isolators. Others have more sophisticated approaches. This can translate to a higher price tag and more maintenance considerations, so it’s important to find a pin box solution from a reputable brand that meets your needs, long-term goals, and budget.

1. Rubber Isolator
   One approach to reducing shock, vibrations, and noise in a 5th wheel connection is with a rubber isolator. Pin boxes with rubber isolators have a pivot point that is cushioned by a piece of rubber, usually sandwiched between two plates of steel. As the plates pivot, their movement is padded and absorbed by the rubber, helping to reduce the effects of jerking and jarring.
2. Gas Strut
   A gas strut is another method of shock-absorption used in 5th wheel pin boxes. Again, the box is equipped with a pivot point or multiple pivot points, allowing the king pin to pivot back and forth. A single gas strut or multiple struts are positioned at the pivot point, limiting and absorbing the movement. This enables the pin box to adapt with the movements of the truck and trailer, while reducing the effects of bumps, rough roads, and crosswinds.
3. Airbag
   Some pin boxes are equipped with airbags. The airbag acts as a cushion between the king pin plate and the rest of the pin box, absorbing chucking, jerking, and road noise between the truck and trailer. This not only means a more comfortable ride for the driver and passengers, but it also promotes longevity for your vehicles and towing equipment.
4. Coil Spring
   An industry-first shock-absorption technology for pin boxes is the coil spring. Developed by CURT, the Helux™ pin box is equipped with a proprietary coil-spring technology that absorbs all manner of shocks, chucking, vibrations, jerking, jarring, and noise like never before. It is also a maintenance-free design, giving it a significant advantage over traditional pin boxes.

One thing to keep in mind when looking for the best pin box for your rig is that many shock-absorbing boxes come with multiple technologies. The Helux, for example, not only uses a coil spring, but it also has an integrated gas strut. Manufacturers design pin boxes with different shock-absorbing components because each component treats road shocks in a unique way, promoting a more comprehensive solution.

Whether you’re purchasing a new 5th wheel trailer or upgrading your existing rig, there are a number of key considerations when it comes to choosing the best 5th wheel pin box for your situation.

Perhaps the most important factor to consider for your pin box is its weight capacity in relation to the rest of your setup. The pin box needs to meet or exceed the towing weight of your trailer. If your trailer weighs 20,000 lbs., you can’t have a pin box rated for only 15,000 lbs.

Additionally, your pin box should be complementary to the rest of your towing system. The rule of thumb is as follows: your towing capacity is always limited to your lowest-rated towing component. This includes your truck, trailer, and all parts of the towing system.

So, for example, you may select a pin box that’s rated for 30,000 lbs., but if your 5th wheel hitch is only rated to 20,000 lbs., your overall towing capacity is still limited to 20,000 lbs.

Also, it’s important to know if your pin box is approved for your particular 5th wheel frame and chassis. Consult the manufacturer before proceeding with a pin box upgrade.

While weight capacity is vitally important to pin box selection, dimensions are a very close second. You need a pin box that will fit your trailer, your hitch, and your truck.

Pin boxes come in various lengths, from short to long. Short pin boxes can measure around 9”, medium pin boxes can measure around 15”, and long pin boxes measure around 20” or more. Make sure the design of the pin box won’t cause obstructions with the layout of your trailer. Additionally, make sure the mounting holes will fit your existing trailer.

The pin box also needs to be a good fit for your truck. Long-bed trucks are compatible with more pin boxes and trailer options, while short-bed trucks may require a more specialized solution, such as a rotating pin box.

Lastly, while most king pins have a standard diameter of 2”, some of the heavier-duty models have a diameter of 3-1/2”. Make sure the king pin on your upgraded pin box will be the right fit for your 5th wheel hitch.

Installing a new 5th wheel pin box is not for the faint of heart. In fact, a professional installation is highly recommended. Pin boxes are heavy (several hundred pounds!) and require precise adjustment and positioning to accomplish smooth, level towing. Unless you have some professional experience and an impressive tool set, pin box installation may not be for you.

Taking your trailer to a professional is a great way to remove the stress of installation and gain some additional insight into the buying decision. The pros can help guide you to a pin box upgrade that will meet the weight capacity requirements, frame / chassis approvals, and dimensional considerations.

Upgrading your 5th wheel pin box from “stock to shock” can be an extremely wise investment, resulting in cost savings long-term. However, that initial investment can be a substantial cost. Before committing to a purchase, make sure you take the time to think things through. You should not only have confident answers to the points made above (weight capacity, dimensions, etc.), but also consider your plans as an RV owner, taking your entire rig and future plans into consideration. Take time to research your options, watch videos, read manuals, read reviews, and talk to other RV owners. Make an informed decision that you’ll be happy about after the fact, for years to come.

Likewise, take time to consider the level of maintenance required for your prospective pin box. Some boxes come with more bells and whistles, but they require more intricate and frequent maintenance long-term. Is the maintenance something you’re equipped and prepared to handle?

Choosing your next 5th wheel pin box shouldn’t be an overnight decision. Do your research! Lippert, as a manufacturer of premium RV and towing products, offers a variety of free resources to help you make an informed buying decision. Check out the pages below to learn more!

• Read manuals and technical documents
• Compare Lippert 5th wheel pin boxes
• Explore the Lippert YouTube channel
• Browse 5th wheel pin boxes
• Contact a local dealer

1. Are all 5th wheel pin boxes the same?
   No, not all 5th wheel pin boxes are the same. Some are designed to provide a simple vehicle-trailer connection and nothing more. Others are more elaborate, incorporating cushion hitch features for improved ride comfort and control. Additionally, pin boxes range in size and weight capacity.
2. Are all 5th wheel king pins the same size?
   There are two basic sizes of 5th wheel king pins. The standard king pin is 2” in diameter. Most 5th wheel hitches on the market today are designed to fit a 2” king pin. For a heavier-duty connection, a 3-1/2” diameter king pin is also available, but this is generally found on commercial trailers, such as semi trailers.
3. Are rotating pin boxes less stable?
   Rotating pin boxes can be less stable than a traditional fixed pin box because they move the truck-trailer pivot point several inches rearward. This can result in the trailer towing more like a classic bumper-pull trailer than a 5th wheel. It is also important to secure the original pivot point (i.e. the king pin connection) with a 5th wheel wedge.
4. Does a 5th wheel king pin need grease?
   The connection point between a 5th wheel king pin and a 5th wheel hitch needs to be lubricated. The traditional method is to use grease. However, grease can be messy and requires frequent reapplication. An alternative to greasing your 5th wheel connection is to use a 5th wheel lube plate. A lube plate is a polyethylene disc that fits over the king pin and acts as a sacrificial buffer between the two surfaces, maintaining smooth articulation over bumps and around turns.
5. What is the best 5th wheel hitch?
   The best 5th wheel hitch for your setup is one that matches your truck layout, towing system capacity, preferences, and budget. Ensuring that your 5th wheel hitch fits the king pin on your trailer is a must, but typically, both will meet the standard 2” diameter. For more information, check out our complete guide to 5th wheel hitches.

Disclaimer: These photographs, recommendations, and approximations are intended for demonstration purposes only and do not reflect the specifications of any particular tow vehicle, recreational vehicle, or trailer. Always consult the manufacturer’s Owner's Manual.