Coil, flat bar and strip: how they differ
A coil is continuous rolled product wound into a coil, strip is that same coil slit lengthwise to the required width, flat bar is a flat rectangular profile supplied in bars, and skelp is narrow strip for roll forming and pipes.
The difference is not in the grade of metal but in the form of delivery, and that is what determines what can be ordered and how the price is calculated.
In the GCX catalogue, coil, flat bar and strip are set out in a separate section; the base sheet product range from which these formats are obtained is 0.8–10 mm, in formats 1250×2500 and 1500×3000, grades 201, 304, 316L and 430.
Coil and strip
Coil is produced on a continuous mill: the metal comes out as a strip and is wound into a coil. Cold-rolled coil gives thin thicknesses and a clean surface, hot-rolled coil gives thick ones and a commercial surface. Coil is convenient for automatic lines: it is unwound, fed into the mill and cut or stamped without stopping.
Strip is a coil that has been slit lengthwise to a specified width. On a single line, several strips of different widths are obtained from a wide coil, so strip is more accurate in width and better suited to specific equipment. It is supplied in coils, less often in loose coils, and is more often counted by weight than by length.
The key parameters of strip are thickness, width, grade, surface, edge condition and the internal diameter of the coil. The internal diameter matters for the uncoiler: if it does not match the axis of the line, the strip will have to be rewound.
| Feature | Coil | Strip | Flat bar | Skelp |
|---|---|---|---|---|
| Delivery form | coil | coil | bars, rods | coil |
| Width | wide | set by slitting | narrow, rectangular section | set for the line |
| Edge | mill edge or cut edge | cut edge | cut edge | cut edge |
| Thickness | thin and medium | thin | medium and up | thin |
| Typical job | stamping, slitting | roll forming, pipes | fasteners, frames, blades | blank for pipes and profiles |
Flat bar and skelp
Stainless flat bar is flat product of rectangular section. Unlike strip, flat bar is supplied not in a coil but in bars of a specified length, and it holds its shape without an uncoiler. Flat bar is used for fasteners, plates, frames, guides, blades and decorative elements, as well as for parts that are more conveniently cut from a bar than unwound from a coil.
Flat bar can be hot-rolled or cold-rolled. Hot-rolled is thicker, its surface is darker and its edge may be rounded. Cold-rolled is thinner and flatter, and easier to grind and polish. A flat bar thickness of 1 mm or less is already thin product, and it is more often obtained by slitting strip.
Stainless flat bar and sheet: what is the difference
Sheet is a wide format, flat bar is narrow. Parts are cut from sheet according to a cutting plan; flat bar is taken at finished width and cut only to length. If the part is narrow and long, flat bar saves time and produces less waste, while if the part is large, it is cheaper and simpler to use sheet.
Skelp is narrow strip obtained by slitting and supplied as a blank for roll forming or pipe. The width of skelp is calculated for a specific line: round or profiled pipe is formed from it, so the edge must be straight and the camber minimal.
In queries such as stainless flat bar 1 mm, stainless flat bar 1mm, stainless steel flat bar and 12х18н10т flat bar, the same flat product is meant: only the thickness, grade and delivery form differ. Stainless steel coil and stainless steel in coils mean coiled strip; 12х18н10т flat bar is an analogue of AISI 321, which is selected as a separate item. When you need to buy stainless steel in coils, buy stainless flat bar or buy flat bar for a cutting plan, the order states the grade, thickness, width and edge condition.
Thicknesses and edges
Thickness and edge are what are most often confused in an order. Thin product of 0.8–3 mm is produced by cold rolling: it goes into strip, flat bar and skelp. Above 3 mm comes hot rolling, and such flat bars and coils go into structures and machining.
An edge can be cut or mill. A cut edge is produced by slitting; it is straight and of the specified width. A mill edge comes straight from the rolling mill: the width varies and the edge may be uneven and defective. An automatic line and roll forming require a cut edge, otherwise the machine will pull the strip off course.
Another parameter is camber, that is, the curvature of the strip along its length. On a short part it is unnoticeable; on a long strip it pulls the strip sideways and spoils the geometry. Flatness and camber are checked at acceptance together with thickness and width.
| Parameter | What to check |
|---|---|
| Thickness | nominal, tolerance, standard |
| Width | specified, edge tolerance |
| Edge | cut or mill |
| Camber | curvature along the length |
| Surface | 2B, BA, №4, mirror |
| Grade | 201, 304, 316L, 430, batch certificate |
What is ordered most often
Strip is more often chosen for roll forming, welded pipes, stamping and automatic lines where continuous feeding and constant width matter. Skelp is for the production of pipes and profiles: it is a blank, not a finished part.
Flat bar is ordered for fasteners, frames, brackets, plates and decorative elements. It is convenient to cut to length and does not need rewinding. Coil is chosen when there is a slitting or stamping line and when the volume justifies working with a large batch.
The grade is chosen by the environment: 201 for dry interiors, 304 for water and food media, 316L for chlorides and chemicals, 430 for dry finishing. Aisi 316 strip is needed where thin material works in a marine environment or in contact with brines.
Frequently asked questions
How does coil differ from strip?
Coil is wide product wound on the mill. Strip is that same coil after slitting to a specified width. Strip is more accurate in width and better suited to specific equipment.
What is skelp?
Narrow strip obtained by slitting and intended for roll forming, most often for the production of pipes and profiles. The width of skelp is calculated for a specific line.
What is 1 mm stainless flat bar?
Thin cold-rolled flat bar of rectangular section, 1 mm thick. It is obtained by slitting strip or by rolling, supplied in bars and used for plates, fasteners and decorative parts.
How does flat bar differ from sheet?
In shape and width. Sheet is a wide format for cutting, flat bar is narrow product of a specified width in bars. Narrow long parts are more economically made from flat bar, large ones from sheet.
How is the weight of a coil or strip calculated?
By the same formula as for sheet: thickness × width × length × 7.9. For a coil the total length of the strip is used, so it is more convenient to calculate by weight and check against the batch certificate.
Is a cut edge needed for roll forming?
Yes. A mill edge varies in width and can pull the strip off course in the mill. For roll forming and automatic lines, strip or skelp with a cut edge and minimal camber is used.
Order coil, flat bar or strip
See the product range and state the grade, thickness, width, edge condition and shipment week in your order.