Fifth Wheel King Pins for Heavy-Duty Trucks & Trailers

The king pin is the pivot and coupling interface between tractor and trailer—ensuring secure, stable connection under heavy loads, shifting dynamics and extreme duty cycles. At Custom Truck One Source, our heavy-duty king pins and associated mounts are built for high-strength, precise fitment and long life in the toughest commercial trucking applications.

Why a Good King Pin Matters

A well spec’d king pin means safe lock-up of the trailer, minimal wear between the pin and upper coupler, controlled lateral/vertical movement and less stress on your fifth-wheel system. High-quality king pins are made from forged alloy steel, heat-treated and precision-machined to resist fatigue, impact and wear—especially under heavy haul, off-road or multi-shift service. A worn or mismatched king pin can cause coupling instability, accelerated component wear, jerky articulation or even separation.

How to Choose the Right King Pin for Your Application

Choosing the right king pin involves several key considerations:

• Size & configuration: Match the king-pin diameter (e.g. 2″, 3.5″), bolt-hole pattern and bolster plate thickness to your trailer’s upper coupler and fifth-wheel plate.
• Material & duty rating: Choose a king pin forged from high-alloy steel, properly heat-treated and tested for wear/resistance (e.g. AISI 4320H or 8630H) for heavy-duty service.
• Mounting & serviceability: Determine if you need a weld-on or bolt-in king pin depending on your trailer design and maintenance preference.
• Application environment: Consider duty-cycle, trailer type (step-deck, low-boy, heavy haul), load shifts and vibration—select a king pin rated accordingly.

If you’re not sure which king pin fits your system, our parts team can help with fitment verification, cross-reference part-numbers and mounting guidance.

Maintenance Tips & Replacement Indicators

To keep your coupling system running smoothly and avoid downtime:

• Check for play or looseness between the king pin and upper coupler, if there’s excessive movement it’s worn.
• Listen for unusual articulating noise, clunking during turns or irregular trailer hitch movement.* Check the mounting area, bolt pattern and bolster plate for fatigue, cracks or distortion—replace the king pin if worn.
• During trailer overhaul or fifth-wheel replacement consider replacing the king pin proactively to ensure full coupling-system reliability.

Why Custom Truck One Source

• Huge inventory of heavy-duty king pins and coupling components for trucks, trailers and equipment.
• Nationwide parts network for fast delivery and minimal downtime.
• Parts experts knowledgeable in heavy-duty truck applications to verify fitment and part numbers.
• Competitive pricing, robust availability and online filters to find the right king pin fast and easy.

Browse & Order Now

Browse our full line of heavy-duty fifth-wheel king pins—filter by diameter, mounting style, part number or duty rating. Order online or call 877-831-0572 for technical support and fitment guidance.