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Sigma Trailer Parts Blog

Trailer Parts Technical Guides

Practical technical resources for trailer manufacturers, fleet operators and parts importers — how to select, install and maintain semi-trailer components.

Drawbar coupling guide - pintle hook coupling

Drawbar Coupling Guide

A-frame vs rigid drawbar types, how to read a coupling eye specification, forged vs cast construction, and the height and maintenance checks that keep a tow coupling safe.

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Fifth wheel coupling guide - cast steel coupling plate

Fifth Wheel Coupling Types Explained

Fixed, sliding, and compensating fifth wheels compared, plus king pin sizing, height selection, and the maintenance checks that keep the coupling safe.

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Slack adjuster guide - automatic brake adjuster arm

Slack Adjuster Types & Adjustment Guide

Automatic vs manual slack adjuster compared, how the mechanism works, correct adjustment angle, and when a Haldex or Meritor unit needs replacing rather than adjusting.

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Trailer axle assembly guide - American type axle with hub and brake

Trailer Axle Selection Guide

A practical breakdown of trailer axle types, capacity ratings, and core components, plus what to check before replacing or sourcing an axle.

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Trailer brake system guide - machined brake drum

Trailer Brake System Guide

How air brakes on a semi-trailer actually work, drum vs disc, S-cam brake components, and a practical trailer brake maintenance checklist.

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Trailer king pin guide - bolt-in king pin

King Pin Guide

2 inch vs 3.5 inch, bolt-on vs weld-on, and how to inspect and measure king pin wear before it becomes a coupling failure.

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Trailer landing gear guide - double speed landing gear

Trailer Landing Gear Guide

Inboard vs outboard, single vs two speed, and how to size landing gear capacity to your trailer — plus the maintenance routine that keeps a crank handle from seizing.

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Trailer leaf spring guide - multi-leaf spring pack

Trailer Leaf Spring Types & Maintenance Guide

Parabolic vs multi leaf spring compared, spring rate and specification explained, plus the failure signs that separate normal wear from a leaf spring about to break.

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Trailer lighting and wiring guide - truck with full lighting at night

Trailer Lighting & Wiring Guide

Trailer LED lighting, reading a wiring diagram, 7 pin plug pinouts, and the ECE and regional light regulations that determine what's legal to run.

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Trailer parts buying guide - suspension brackets in warehouse

Trailer Parts Buying Guide

A practical walkthrough of sourcing, quality inspection, MOQ, mixed container loading, and shipping when buying trailer parts from a Chinese manufacturer.

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Trailer suspension guide - bogie tandem mechanical suspension

Trailer Suspension Guide

How trailer suspension works, mechanical vs air suspension, bogie and walking beam designs, core parts, and a maintenance checklist.

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Trailer tire guide - semi-trailer tires on chrome rims

Trailer Tire Size & Maintenance Guide

11R22.5 vs 12R22.5 compared, how to read load and speed ratings, and the tire wear patterns and pressure habits that separate a tire that lasts from one that fails early.

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Trailer U-bolt guide - heavy duty U-bolt for leaf spring

U-Bolt & Fastener Guide

Reading a u bolt specification, correct spring u bolt torque, axle u bolt sizing, grade 8.8 fastener strength, and when to replace a center bolt.

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Trailer wheel rim guide - polished aluminum alloy rim

Trailer Wheel & Rim Guide

Trailer wheel rim sizes, tubeless vs tube type, steel vs aluminum, hub pilot vs stud pilot, bolt patterns, and torque specs explained.

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Turntable slewing ring guide - trailer bearing ring

Turntable & Slewing Ring Guide

How a trailer turntable's slewing ring bearing works, how to size load capacity, and the lubrication and maintenance routine that prevents premature wear.

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Container twist lock guide - semi-automatic twist lock

Twist Lock & Container Lock Guide

Manual, semi automatic, and fully automatic twist lock types compared, plus the ISO standard and installation checks that keep a container locking mechanism secure.

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