Inspection method of wire rope diameter

Accurate wire rope diameter inspection is essential for ensuring the safety and performance of lifting equipment such as electric wire rope hoists. Because the cross-section of a wire rope is not perfectly circular, an incorrect measuring position can easily lead to inaccurate results. This article explains how to correctly measure wire rope diameter using a vernier caliper, along with important handling and usage precautions.

1. How to Measure Wire Rope Diameter Correctly

When performing wire rope diameter inspection, always measure at the maximum diameter position of the rope. 

Since the rope is composed of strands twisted together, its cross-section may appear slightly irregular, and measuring at the wrong angle may produce a smaller value than the actual diameter.

Examples of Wire Rope Specifications for CD-Type Electric Hoists

• 0.25 t hoist: 6×19–3.6

• 0.5 t hoist: 6×37–4.8–180

• 1 t hoist: 6×37–7.4–180

• 2 t hoist: 6×37–11–155

• 3 t hoist: 6×37–13–170

Using the 0.25 t hoist as an example:

6 → The rope is made of 6 strands

19 → Each strand contains 19 wires

3.6 → The rope’s nominal diameter is 3.6 mm

This numbering helps technicians quickly identify rope structure and diameter before conducting a wire rope diameter inspection.

2. Precautions When Using a Vernier Caliper for Wire Rope Diameter Inspection

(1) Proper Handling of the Vernier Caliper

• Treat the caliper as a precision instrument—handle it gently and avoid impacts or dropping.

• Do not measure rough or abrasive surfaces to prevent damage to the measuring jaws.

• Keep it away from sharp tools that may scratch its surface.

• Store it in a clean, dry, neutral environment; avoid acidic or alkaline conditions that may cause corrosion.

(2) Clean and Zero the Caliper Before Measuring

Before starting the wire rope diameter inspection:

• Wipe the measuring surfaces clean.

• Ensure the jaws and edges are straight and undamaged.

• Close the jaws completely—there should be no visible gap.

• Check that the zero lines of the main scale and vernier scale align.
  This procedure is called zero calibration and ensures measurement accuracy.

(3) Smooth Movement and Proper Locking

• The slider should move smoothly without being too loose or too tight.

• After locking the screw, the reading must remain stable.

• Always loosen the screw before moving the slider—do not force it.

(4) Apply Proper Measuring Pressure

When measuring the diameter:

• The jaws should just contact the rope surface—avoid excessive force.

• Too much pressure may deform the jaws or the rope, leading to inaccurate readings
  (outer dimensions appear smaller and inner dimensions appear larger).

(5) Correct Reading Technique

• Hold the caliper horizontally and face a bright light source.

• Keep your line of sight perpendicular to the scale to avoid parallax errors.

(6) Measure Multiple Positions for Accuracy

To ensure a reliable wire rope diameter inspection:

• Measure the rope several times from different directions on the same cross-section.

• For longer ropes, take measurements at multiple locations along its length.
  This helps obtain a more accurate and representative result.

Accurate wire rope diameter inspection is critical for maintaining equipment safety and preventing premature wear or failure. By measuring at the rope’s maximum diameter and properly using a vernier caliper, technicians can ensure reliable results and extend the service life of wire ropes in lifting applications.

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