Metal Service Center Glossary: Slitting and Coil Processing Terms
Plain definitions of the terms used on a slitting line and in coil planning: trim loss, nesting, PIW, mults, coil genealogy, toll processing and more.
Bilal Yousuf
September 2, 2026
Quick answer
An operator's glossary of the vocabulary used around a coil slitting line and the planning desk behind it: material and coil terms, processing terms, planning and optimization terms, and the business and data terms that carry a coil through an order. Each entry gives a definition and one line on how it moves yield or margin.
Most of these words are defined somewhere: a vendor brochure, a mill spec sheet, a research paper. Harder to find is all of them in one place, defined the way a scheduler and a line operator actually use them.
Material and coil
Master coil
A master coil is the full-width, full-weight coil as it arrives from the mill, before any processing. Flat-rolled masters commonly run somewhere between 36 and 72 inches wide, at weights in the tens of thousands of pounds, though both vary by mill and product. Everything a service center ships is cut from one, and the master is the unit that gets bought, inventoried and certified.
Why it matters: every dollar of scrap is measured against the master coil you consumed for the order.
Mult
A mult (short for "multiple") is one of the narrower coils produced when a master coil is slit. A pass across a 60-inch master might yield four 14-inch mults plus edge trim. Also called strips or slits, they are what ships to the customer or feeds the next process.
Why it matters: how many mults fit across the width, and how little is left over, is the yield question in one number.
Gauge
Gauge is material thickness, quoted in decimal inches (0.030", 0.125") or millimeters outside North America. Older gauge-number scales still appear on drawings, but they differ by metal and are not interchangeable. Gauge is the hardest compatibility constraint in planning: coils of different thickness cannot run together in one setup.
Why it matters: gauge splits your order book into groups that can never be combined, which is what makes the planning problem large.
PIW (pounds per inch of width)
PIW is coil weight divided by coil width. A 20,000-pound coil 40 inches wide is 500 PIW. It normalizes weight so coils of different widths compare directly and equipment limits state once. Customers order to PIW ranges because it sets how long a coil runs on their press before a changeover. See Rolled Metal Products' PIW calculator.
Why it matters: a mult that misses the customer's PIW window is a reject even if the width and gauge are perfect.
ID and OD
ID is the inside diameter of the coil eye, the hole the mandrel goes through, typically 16, 20 or 24 inches. OD is the outside diameter of the wound coil. Both are set by the equipment on each end: your recoiler and the customer's uncoiler.
Why it matters: an OD beyond the customer's uncoiler capacity forces a rewind, which is unpaid handling you did to yourself.
Coil weight
Coil weight is the mass of a coil, in pounds or tonnes, as received from the mill or as calculated for a mult after slitting. Mult weight is derived from master weight in proportion to width, less trim and any material lost to defects.
Why it matters: weight is the billing unit for most flat-rolled material, so weight accuracy is revenue accuracy.
Grade
Grade names the metal's chemistry and mechanical properties: CS Type B, HSLA 50, 304 stainless, 3003-H14 aluminum. It is written into the order and certified by the mill. Grades are not substitutable without customer approval, even when dimensions match.
Why it matters: grade is a second hard partition on top of gauge; together they decide which orders can ever share a coil.
Edge condition
Edge condition describes how the strip edges are finished: mill edge (as rolled, untrimmed), slit edge (sheared during slitting), or deburred, rounded or squared edges from extra tooling. Tube mills, roll formers and anything handled by hand specify it explicitly.
Why it matters: a specified edge condition can force a slitting pattern you would not otherwise choose, and can rule out running a mult from a mill-edge position.
Camber
Camber is sideways curvature along the length of the strip. One edge is longer than the other, so a length laid flat bows away from straight. It arrives from the mill or is introduced during slitting when knife clearance differs across the arbor. Ulbrich covers the measurement convention.
Why it matters: cambered mults wander in the customer's press and come back as claims, which turns a good yield number into a bad month.
Crown
Crown is a thickness profile across the width of the strip, thicker at the center than at the edges, as rolled. A small amount is normal and intentional; too much means mults slit from the center run heavier than those slit from the edges.
Why it matters: crown makes position across the master coil matter, so two mults of identical ordered width are not identical products.
Slitting and processing
Slitting
Slitting is cutting a coil lengthwise into narrower coils through a set of rotating circular knives. The coil is uncoiled, passed through the knife stand, separated, tensioned and rewound as multiple mults on one recoiler shaft. It is the highest-volume first-stage process at most service centers.
Why it matters: slitting is where width decisions become irreversible, which is why the plan behind it is worth more than the machine.
Cut-to-length
Cut-to-length (CTL) uncoils material, levels it, and shears it crosswise into sheets or blanks of a specified length. Where slitting cuts width, CTL cuts length. Many service centers run both, and a master coil may be slit first and cut-to-length after.
Why it matters: CTL demand competes with slitting demand for the same inventory, so the two lines cannot be planned in isolation.
Knife setup and tooling
The knife setup is the arrangement of circular knives, spacers and rubber stripper rings mounted on the arbors to produce a specific set of widths. Spacers are ground to precise thicknesses and the stack must total the arbor's usable length. Building one is skilled manual work.
Why it matters: setup time is the real cost of variety, so a plan ignoring tooling changes optimizes the wrong thing.
Arbor
The arbor is the shaft carrying the knives and spacers through the slitter head, one above the strip and one below. Its usable length caps the total width of material plus tooling you can run; its diameter and material set the maximum gauge the head can cut.
Why it matters: arbor space is a hard constraint that quietly rules out otherwise attractive combinations of orders.
Edge trim
Edge trim is the narrow ribbon removed from each side of the master coil so the outer mults have clean, dimensionally accurate slit edges rather than mill edge. Typical trim is a quarter inch to an inch per side, depending on the mill's width tolerance and incoming edge quality.
Why it matters: trim is guaranteed loss on every coil, so it belongs in the yield math from the first calculation, not as an afterthought.
Multi-pass
Multi-pass runs the same material through a line more than once: slitting a wide master into intermediate widths, then re-slitting those into final mults. It is used when final widths are too narrow to run stably in one pass, or when the arbor will not hold the stack.
Why it matters: every extra pass adds handling, adds a second chance to introduce camber, and consumes line hours you cannot bill twice.
Remnant and drop
A remnant, also called a drop, is usable material left over after the ordered mults are cut: a width nobody asked for, wound and put back into inventory. It is not scrap: it has a tag, a weight, and a chance of matching a future order.
Why it matters: remnants that never find a home are working capital slowly turning into scrap value, so how aggressively you create them is a real decision.
Skidding
Skidding is banding, wrapping and mounting finished mults on skids or coil cradles for shipment, including edge protectors, desiccant and any specified packaging. It happens at the exit end of the line and is often the bottleneck when many narrow mults come off one master.
Why it matters: a pattern that produces twenty narrow mults may be mathematically excellent and still back up the packaging crew for a shift.
Line speed
Line speed is how fast material runs through the slitter, in feet per minute. It falls with thicker gauge, harder grades, more knives in the stack, and tighter tolerance work. Real throughput is line speed less setup and threading time between coils.
Why it matters: two plans with identical yield can differ by hours of line time, and line time is the capacity you are actually selling.
Toll processing and outside processing
Toll processing is performing a processing service on material the customer owns, for a fee, rather than selling from your own inventory. Outside processing is the same arrangement from the other side: sending your material to a shop with equipment you lack. Worthington Steel matches common trade usage.
Why it matters: toll coils occupy inventory, tags and line hours but carry no material margin, so they must be planned and costed differently.
Planning and optimization
Cutting-stock problem
The cutting-stock problem is the classical operations research question of cutting smaller ordered pieces from larger stock at minimum waste. Gilmore and Gomory formalized it in 1961 and introduced column generation to solve it. Coil slitting is the one-dimensional version, complicated by real inventory, compatibility rules and due dates.
Why it matters: the textbook version assumes unlimited identical stock; your version has 400 specific coils with specific certs, which is why generic solvers disappoint.
Nesting and patterns
A pattern is one arrangement of ordered widths across a coil, such as 14" + 14" + 14" + 14" + trim across a 60" master. Nesting is choosing those arrangements. A full order book generates millions of feasible patterns across the available coils.
Why it matters: nesting is where scrap is decided; every downstream number is a consequence of which patterns you chose.
Trim loss
Trim loss is material leaving the line as unusable width: the edge trim off each side, plus any width left over because the ordered mults did not sum to the coil width. It is expressed as a percentage of master coil weight. Reducing it is the core objective of slitting optimization. Our 12-point checklist covers the levers that move it.
Why it matters: at high service center volumes, a single percentage point of trim loss can be six figures of material a year. Run the arithmetic on your own tonnage and cost per ton.
Yield
Yield is the share of input material leaving as saleable product, by weight: shipped pounds divided by consumed pounds. It is the inverse of total loss: trim, scrap, defect rejections and unclaimed remnants all reduce it.
Why it matters: yield is the one number that combines the planner's decisions and the line's execution, which is why it is the honest scoreboard.
Scrap rate
Scrap rate is the share of consumed material sold at scrap value rather than product value, as a percentage of input weight. Its causes split in two: planned scrap, which is the trim you knew you would take, and unplanned scrap from defects, mis-slits and short runs.
Why it matters: the two halves have different fixes, and reporting them as one number hides which problem you actually have.
Width tolerance
Width tolerance is the permitted deviation from ordered width, quoted as a plus and minus band (+0.010" / -0.000"). It is set by the customer's application and reflected in how the knife setup is built and how mults are gauged during the run.
Why it matters: tight tolerance narrows which combinations can run together and raises the cost of getting the setup wrong.
Must-ship order
A must-ship order is one the plan cannot leave behind: a contractual commitment, a line-down customer, a due date at the edge. Planners mark these before optimizing, and the plan must cover them even at a yield penalty.
Why it matters: the highest-yield plan that misses a must-ship order is not a plan you can run, so this constraint has to be inside the optimization and not applied afterwards.
Partial coverage
Partial coverage is filling part of an ordered quantity now and leaving the balance for a later run. It is normal, because orders rarely divide neatly into coils, but it has to be tracked: the remainder becomes tomorrow's constraint.
Why it matters: untracked partials cause double-shipping and phantom shortages, both costlier than the yield you gained by splitting the order.
Slitting plan and schedule
A slitting plan is the instruction set for a period of production: which coils to pull, which patterns to cut from each, which orders each mult satisfies, in what sequence. It is the output of nesting, ordered for the line. LineSight builds these from live order and inventory data and returns them to the ERP as work orders. From PO to release shows where the plan sits in the wider flow.
Why it matters: the plan is the artifact where yield, due dates, setups and capacity are reconciled, or where they quietly are not.
Knife change
A knife change is teardown and rebuild of the tooling stack when the next coil requires a different set of widths. Depending on the line and the setup it can take anywhere from a few tens of minutes to well over an hour, during which the line produces nothing.
Why it matters: sequencing coils so similar setups run together converts pure downtime into production, which is often worth more than the last half-point of yield.
Business and data
Metal service center
A metal service center buys metal from mills in bulk, holds inventory, performs first-stage processing such as slitting and cut-to-length, and sells to manufacturers in the sizes and quantities they need. MSCI, the industry's trade association, represents several hundred member companies across North America.
Why it matters: the business model is buying wide and selling narrow, so the conversion between the two is where the margin lives.
Coil genealogy and tags
Coil genealogy is the recorded lineage of every piece of material: which master it came from, which heat and mill cert stand behind it, which mults were slit from it, which remnants remain. Each coil carries a tag number anchoring that chain in the ERP.
Why it matters: without intact genealogy you cannot answer a customer's claim or a recall question, and in certified applications that ends the relationship.
Work order
A work order is the shop-floor instruction to process a specific coil a specific way: coil tag, pattern, resulting mults, line, target date. It is the bridge between plan and machine, and the record against which production is reported back.
Why it matters: if the plan does not become work orders automatically, the plan's quality is capped by how fast someone can retype it.
Release
A release is an authorization to ship a defined quantity against a larger standing order or blanket contract. Customers on annual agreements release material in weekly or monthly increments, so shippable demand is the releases, not the contract total.
Why it matters: planning against contract quantities instead of releases builds inventory nobody asked you to build.
Mill certs and MTRs
A mill test report (MTR), or mill test certificate, is the mill's document certifying a coil's chemistry and mechanical properties against the ordered specification, tied to a heat number. EN 10204) defines the certificate types, of which 3.1 is standard in steel. Certs follow the material to every mult.
Why it matters: a mult without a traceable cert is unsellable to a certified customer regardless of its dimensions.
RFQ
An RFQ (request for quotation) is a customer's request for pricing on specified material: grade, gauge, width, quantity, tolerance, packaging, delivery. Quoting it well means knowing what it will actually cost to produce, which depends on what else you are cutting that week.
Why it matters: quoting from a standard cost instead of a real yield estimate is how service centers win the jobs they should have lost.
ERP
The ERP is the system of record: orders, inventory, tags, work orders, shipments, invoices. It answers questions with one true answer: what is in stock, what shipped, what is owed. It is not a planning system, and asking it to nest patterns is asking the wrong tool.
Why it matters: planning lives next to the ERP, not inside it. That is why LineSight's Command Center reads live orders and inventory from the ERP and writes plans, work orders and updates back.
Frequently asked questions
What is trim loss in coil slitting?
Trim loss is material that leaves a slitting line as unusable width rather than saleable product. It has two parts: the edge trim removed from each side of the master coil to give the outer mults a clean slit edge, and the leftover width when the ordered strips do not add up to the coil's usable width. It is reported as a percentage of master coil weight, and reducing it is the main objective of slitting optimization.
What is the difference between a master coil and a mult?
A master coil is the full-width, full-weight coil as it arrives from the mill, before any processing. A mult, short for "multiple", is one of the narrower coils produced when that master is slit lengthwise. One pass across a wide master produces several mults plus edge trim. The master is the unit you buy, inventory and certify; the mults are what ship to customers or feed the next process.
What does PIW mean on a steel coil?
PIW stands for pounds per inch of width, and it is coil weight divided by coil width. A 20,000-pound coil 40 inches wide is 500 PIW. It normalizes weight so coils of different widths compare directly, which lets equipment limits be stated once. Customers order to PIW ranges because PIW sets how long a coil runs on their press before a changeover.
What is coil genealogy and why does it matter?
Coil genealogy is the recorded lineage of every piece of material: which master coil it came from, which heat and mill certificate stand behind it, which mults were slit from it, and which remnants remain. Each coil carries a tag number anchoring that chain in the ERP. Without intact genealogy you cannot answer a customer claim or a recall question, and in certified applications that ends the relationship.
What is toll processing?
Toll processing is performing a processing service, such as slitting or cut-to-length, on material the customer already owns, for a fee, rather than selling material from your own inventory. Outside processing is the same arrangement seen from the other side: sending your own material to a shop with equipment you do not have. Toll coils occupy inventory, tags and line hours but carry no material margin, so they have to be planned and costed differently.
What is nesting in slitting optimization?
Nesting is choosing which combination of ordered widths to cut across each coil. Each combination is a pattern. A full order book generates millions of feasible patterns across the available coils, which is why nesting is a search problem rather than a lookup, and why it is usually where scrap is decided. Every downstream yield number is a consequence of which patterns were chosen.
Bilal Yousuf is co-founder of LineSight, which builds production planning software for metal service centers. If you are evaluating tools in this category, our buyer's guide sets out the questions worth asking.