8903 Dunbier H3263 Mackay 2 1/4 x 7/16 Mechanical Caliper Bolt, Washer and Spring Washer | Marine Trailer Part

🔧 Product Description

Dunbier Grade 8 Mechanical-Caliper Bolt 7/16" UNF × 2-1/4" – Part Number: 8903

A replacement 7/16" UNF × 2-1/4" trailer fastener supplied in a zinc-plated grade 8 steel configuration. It is intended for Dunbier/Mackay mechanical disc-caliper mounting and should only replace hardware with the same dimensional, thread and strength specification.

⚙️ Key Features

• 7/16" UNF fastener diameter
• Nominal length: 2-1/4"
• zinc-plated Grade 8 steel finish/material
• Hex-head trailer fastener
• Suitable for marine trailer servicing when matched to the original installation
• Matching matching flat washer and spring washer set supplied

📏 Specifications

• Diameter/thread: 7/16" UNF
• Nominal length: 2-1/4"
• Thread form: 7/16-inch UNF
• Strength requirement: Grade 8 high-tensile
• Finish/material: zinc-plated Grade 8 steel
• Catalogue grade: Grade 8
• Brake-caliper fastener; use no unverified substitute

🔄 Cross Reference & Related Parts

• Dunbier: 8903
• Mackay: H3263
• A generic replacement is acceptable only when diameter, length, thread pitch, strength grade, finish and shank configuration all match
• Do not substitute lower-grade hardware or an unverified stainless bolt in a high-tensile structural application

🚤 Trailer Compatibility & Application

• Suitable for Dunbier/Mackay mechanical disc-caliper mounting
• Measure the original bolt from beneath the head to the end of the thread unless the fastener standard states otherwise
• The unthreaded grip length must suit the clamped joint and must not bottom the nut before the components are secure
• Use the correct washer, locking nut or spring washer for the original joint

🔌 Function

Clamps the associated trailer components together and transfers shear, tension and vibration loads through the mounting joint.

⚠️ Common Signs of Failure

• Thread is stretched, crossed, stripped or heavily corroded
• Bolt shank is bent, necked, grooved or worn
• Hex head is rounded or cracked
• Joint repeatedly loosens despite correct torque and locking hardware
• Corrosion has materially reduced the fastener diameter

🛠️ Installation & Safety

• Confirm the replacement grade from the original bolt head and trailer parts documentation
• Do not reuse a fastener that has stretched, yielded or suffered severe corrosion
• Tighten to the specification for the exact bolt grade, thread, finish and joint
• Use corrosion-compatible washers and locking hardware
• Recheck critical trailer fasteners after the first trip and during routine servicing

📦 Condition

• Brand new Dunbier Marine Products trailer component
• Supplied as one caliper bolt with flat and spring washers
• Supplied in original or equivalent packaging