• 12 parts
  • Checked September 2026

Parts of a 5th Wheel

The fifth-wheel coupling first, then the front of the trailer named after it.

Parts of a 5th Wheel

Name Date

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1 2 3 4 5 6 7 8 9 10 11 12
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Write the name of each numbered part.Answer key

  1. Top plate (skid plate)
  2. Locking jaws
  3. Release handle
  4. Mounting brackets
  5. Slider
  6. Kingpin
  7. Pin box
  8. Breakaway switch
  9. 7-way cord
  10. Landing gear
  11. Slide-out
  12. Stabilizer jacks

Drawn for this site on 2026-09-30 from plain geometry. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

Next step Next: the ball hitch at the bumper

All 12 parts on the diagram

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The coupling 6

  1. Top plate (skid plate) Kept greased so the trailer's plate can turn on it. The plate turns as the truck steers.
  2. Locking jaws They close around the shank of the kingpin. They hold the trailer to the truck.
  3. Release handle Pulling it to the open position unlocks the jaws. The truck can then drive out from under the trailer.
  4. Mounting brackets The plate is pinned to them and can tilt. Before coupling it tilts down toward the rear.
  5. Slider A sliding fifth wheel can be moved forward or back along it. It is moved, then locked, to change how the load sits on the truck's axles.
  6. Kingpin A steel pin under the front of the trailer. It slides up the slot and the jaws lock around it.

Fifth-wheel trailer 6

  1. Pin box Goes onto the hitch in the truck bed. It is part of a fifth-wheel trailer, and the kingpin is on its underside.
  2. Breakaway switch Puts the trailer's brakes on if the trailer comes loose. Its cable is fixed to the truck.
  3. 7-way cord Carries power from the truck for the trailer's brakes and lights. It has a 7-pin plug.
  4. Landing gear The front jacks; they are raised all the way before towing.
  5. Slide-out A room section that extends out from the side when parked. It is pulled back in for towing.
  6. Stabilizer jacks They steady the trailer while people are inside. They are not for leveling or lifting it.

How this list was compiled: Part names checked on 2026-09-30, a name kept only when two independent sources use it. The coupling: (1) Commercial Driver's License Manual (AAMVA model manual, Texas edition DL-7C), sections 6.4, 6.5 and 11.6, https://www.dps.texas.gov/internetforms/Forms/DL-7C.pdf (fifth wheel skid plate, locking jaws, release handle and release arm, kingpin, sliding fifth wheel and its locking pins, landing gear, the plate greased, the wheel tilted down toward the rear before coupling); (2) JOST International, fifth wheel catalog LT SKCAT-01, https://jostinternational.com/hubfs/5th-Wheel-Catalog-LT-SKCAT-01.pdf (topplate, lock jaw, locking bar, release handle, bracket and bracket pin, mounting brackets, slide bracket, slide rail, air slider, kingpin); (3) Fontaine Fifth Wheel catalogue, June 2025, https://fontainefifthwheel.com/cms/wp-content/uploads/2025/07/EN_Fontaine_Catalogue_Jun25.pdf (top plate, jaw, lockbar, release handle, mounting bracket, slider base, kingpin); (4) Wikipedia, Fifth-wheel coupling (kingpin, horseshoe-shaped fifth wheel, grease, the origin of the name) and Caravan (trailer), section Fifth-wheel trailer. The trailer: (5) Keystone RV Company Owner's Manual, 2021, https://keystonerv-prod.zaneray.com/cms/media/136c084c-9d67-4d4a-8f4d-e63b6ccb3070_2021+Keystone_owners_manual.pdf (pin box, kingpin, landing gear jacks, breakaway switch, 7-way cord and 7-pin plug, slide-out, stabilizer jacks); (6) Jayco Towable Owner's Manual, https://www.jayco.com/uploads/rvs/manuals/659-Towable-Manual---Book-2027.pdf (pin box, king pin, landing gear, breakaway switch, 7-way plug, slideout, stabilizer jacks). Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no maker's coupling or trailer, nothing traced. Licence: own work

How it works

A fifth wheel is the plate-and-pin coupling that joins a semi-trailer to its truck. A smaller one in a pickup bed pulls the camper trailer that took its name. The first view is the coupling; the second is the front of that trailer.

Read the full guide

How the coupling locks

The truck backs under the front of the trailer. The kingpin slides along the slot in the top plate, and when it reaches the middle the locking jaws close around its shank. To uncouple, the driver pulls the release handle to open the jaws and drives forward. The plate is greased so the trailer can turn on it.

  • After coupling, a driver looks into the back of the fifth wheel to see that the jaws closed around the kingpin's shank, not its head.
  • This page names the parts; it does not sell them.

Questions and answers

What are the parts of a 5th wheel hitch?

The top plate, also called the skid plate, which the trailer rests on; the locking jaws that close around the kingpin; the release handle that opens them; and the mounting brackets that hold the plate. A sliding fifth wheel sits on a slider.

What is the pin on a fifth wheel trailer called?

The kingpin. On a semi-trailer it is a steel pin under the front of the trailer. On a fifth-wheel camper it is on the underside of the pin box, the frame under the raised front.

Why is it called a fifth wheel?

The name comes from a similar coupling on four-wheeled horse-drawn carriages and wagons, which let the front axle assembly pivot for turning.

What is landing gear on a fifth wheel?

The legs that hold up the front of the trailer when it is not on the truck. They are raised all the way before towing. The small jacks at the corners are stabilizer jacks, which only steady the trailer when parked.

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