Fish Bolts Industrial

Product Description

Fish bolts (also known as track bolts) are specialized heavy-duty fasteners used in the rail industry and heavy-track crane systems. Their primary purpose is to secure fishplates (joint bars) to the ends of two rail sections, connecting them into a continuous track.

Because rail systems undergo extreme thermal expansion, intense vibration, and massive vertical loads, these bolts are engineered with specific mechanical properties that differ from standard structural hardware.

Key Design Features

• Elliptical or Oval Neck: Unlike standard bolts with square necks, fish bolts often have an oval or elliptical shape just below the head.

  • Purpose: This prevents the bolt from rotating when the nut is tightened or loosened, even if the bolt is heavily rusted or weathered. The rail fishplate has a matching oval hole to lock it in place.

• Head Shape: They typically feature a button head or a hemispherical head. This rounded profile minimizes catch points and is designed to withstand the side-thrust forces of passing wheel flanges.

• Thread Fit: They are usually manufactured with a "heavy" thread fit to accommodate the environmental debris and high-torque requirements of track maintenance.

Mechanical Grades and Standards

Fish bolts are safety-critical components and must adhere to strict international standards such as ASTM A183 or ISO 898-1.

Essential Components of the Joint

A fish bolt is rarely used alone; it is part of a specialized fastening assembly:

1. The Bolt: Often coated in black oxide or hot-dip galvanized for corrosion resistance.

2. Spring Washers: High-tension helical spring washers are mandatory. They maintain clamping pressure despite the constant vibration and the natural "settling" of the rail joint.

3. Heavy Hex Nuts: Large nuts that provide enough surface area for high-torque track wrenches.

Technical Considerations

1. Thermal Expansion

Rail tracks expand and contract significantly with temperature changes. Fish bolts must be tightened to a specific torque that allows the rail ends to slide slightly within the fishplate without the joint becoming "frozen" or loose.

2. Shear Forces

The primary stress on a fish bolt is shear. As a train passes over a joint, the rail ends want to move vertically and horizontally. The bolt shank must be sized precisely to the hole diameter of the fishplate to minimize impact wear.

3. Maintenance

In industrial environments—such as ports, mines, or steel mills—fish bolts are often subjected to chemical corrosion. Using stainless steel or specialized coatings (like Dacromet) is common in these specific sectors to prevent the bolts from seizing, which would make track repairs nearly impossible.

Common Sizes

While custom sizes exist for older industrial tracks, the most common diameters for modern systems include:

• Metric: M20, M22, and M24.

• Imperial: 3/4", 7/8", and 1".