Jun 10, 2026 · 5 min read

Galvanized Steel Coil Inner Diameter 508 vs 610: Which ID to Choose

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galvanized steel coil inner diameter 508 vs 610 steel coil - ChinaCNU Steel

Understanding Inner Diameter in Galvanized Steel Coils

The inner diameter of a galvanized steel coil refers to the hollow center hole through which the coil mounts on a mandrel. Standard IDs in the industry are 508mm (20 inches) and 610mm (24 inches). The choice affects coil weight, outer diameter, and how the coil behaves during unwinding. For hot dip galvanized coil, the ID must match the uncoiler expansion range to avoid slippage or damage to the zinc coating.

508mm ID Coils: Compact and Cost-Effective

Coils with a 508mm inner diameter are common in markets where space is limited. They allow for tighter winding, resulting in a smaller outer diameter for the same weight. This makes them ideal for narrow slitting lines and manual handling. However, the smaller ID creates higher tension during unwinding, which can be problematic for thin-gauge GI coil with light zinc coating Z60.

610mm ID Coils: Heavy-Duty and Stable

The 610mm ID is preferred for large-volume processing and heavy-gauge galvanized steel coil. The larger bore reduces coil curvature and provides more stable unwinding, especially for thick materials above 2.0mm. This size is standard in many automated stamping and roll-forming lines. For galvanized steel supplier shipments, the 610mm ID often allows higher coil weights without exceeding truck weight limits.

Key Differences Between 508mm and 610mm Inner Diameter

Choosing between these IDs involves trade-offs in coil weight capacity, handling equipment, and shipping efficiency. Below is a data comparison table based on typical galvanized steel coil specifications from ChinaCNU Steel.

Parameter	508mm ID (20 inch)	610mm ID (24 inch)
Maximum coil weight	Up to 5 tons per coil	Up to 10 tons per coil
Common outer diameter	1200–1400mm	1400–1800mm
Zinc coating range	Z60–Z275	Z60–Z275
Typical thickness range	0.12mm–2.0mm	0.12mm–3.0mm
Uncoiler mandrel size	500–520mm	600–620mm
Shipping container efficiency	More coils per container	Fewer coils but higher tonnage
Preferred for	Narrow slitting, manual lines	Automated stamping, heavy gauge

Zinc Coating Compatibility with Different IDs

The zinc coating weight—whether Z60, Z120, or Z275—does not directly dictate the inner diameter choice, but it influences handling. For light zinc coating Z60 (60g/m²), the thinner coating is more susceptible to edge damage during unwinding. A 610mm ID reduces bending stress, protecting the coating. For heavy Z275 coating used in corrosive environments, both IDs work, but the larger ID minimizes cracking risk during slitting.

Processing Considerations for Hot Dip Galvanized Coil

Hot dip galvanized coil produced via the Sendzimir process has a uniform coating. When selecting ID, consider your uncoiler’s expansion range. A 508mm ID requires a mandrel that expands to at least 500mm, while 610mm needs 600mm. Mismatched IDs cause coil wobble, leading to scratches on the GI coil surface. Always verify your equipment specifications before ordering.

Shipping and Logistics for 508mm vs 610mm Coils

FOB pricing from the factory in Boxing, Binzhou varies with ID due to packing and container utilization. A 20-foot container can hold approximately 10–12 coils of 508mm ID (1.0mm thickness) versus 8–10 coils of 610mm ID. However, the 610mm coils carry more steel per coil, often reducing per-ton freight costs. For MOQ 25 tons, we recommend mixing IDs to optimize container space. ChinaCNU Steel offers both sizes with standard eye-to-sky or eye-to-side orientation.

Export Experience with Global Buyers

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FAQ: Galvanized Steel Coil Inner Diameter 508 vs 610

1. Can I use a 508mm ID coil on a 610mm uncoiler?
No. The coil will not fit on the mandrel. Using a smaller ID on a larger mandrel can damage the coil bore and cause unwinding issues. Always match the ID to your uncoiler size.

2. Which inner diameter is better for thin gauge galvanized steel coil?
For thickness below 0.5mm, 610mm ID is recommended. The larger diameter reduces coil set and prevents material distortion during unwinding. Thin GI coil with 508mm ID may experience edge wave.

3. Does inner diameter affect zinc coating quality?
Indirectly. A mismatched ID can cause vibration during unwinding, which may scratch the zinc coating. Both IDs are compatible with Z60 to Z275 coatings if handled properly.

4. What is the standard inner diameter for hot dip galvanized coil in China?
Chinese mills commonly produce both 508mm and 610mm IDs. The 508mm is more prevalent for domestic construction, while 610mm is standard for export to heavy industries. ChinaCNU Steel supplies both from our factory in Boxing, Binzhou.

5. How does coil weight limit ID selection?
Heavier coils above 8 tons typically require 610mm ID to maintain structural integrity during lifting and shipping. Lighter coils under 5 tons can use 508mm ID. Our MOQ 25 tons can be split into multiple coil weights.

How to Order the Right Galvanized Steel Coil

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