What exactly is the 4-point inspection system and what does it measure?
Fabric inspection is the recording of visual and dimensional defects by passing the rolls across a lit inspection table before shipment. The name "4-point" comes from the maximum score that can be assigned to any defect being 4: a small stain is given 1 point and a large hole 4 points. The aim is not to ignore the defect but to weigh it - so that, instead of subjective statements such as "there are a lot of defects", a single threshold value agreed between buyer and seller (points/100 square yards) is discussed.
Unlike the other laboratory tests covered in the quality and testing guide (fastness, shrinkage, pilling), this system measures visual integrity; for example colour fastness or abrasion resistance are assessed by separate tests. The 4-point inspection does not replace these, it complements them.
Typical defects in knitted fabric are yarn break/drop stitch, streak/course difference (barré), holes, stains, oil marks, needle lines and dye-related listing (abraj). In the knitting, dyeing and printing flow, the source of these defects may be any of the knitting, finishing or dyeing stages; inspection also helps trace back which stage the problem came from.
How many points are given according to defect size?
Scoring is based on the longest measurement of the defect on the fabric; direction (length or width) does not change the score, only the length is taken into account. The table below summarises the standard 4-point thresholds. Since inch values are the reference unit in the industry, the centimetre equivalents are given approximately.
| Defect's longest dimension | Approximate metric equivalent | Points awarded |
|---|---|---|
| 3 inches and under | ≤ 7.5 cm | 1 point |
| 3 inches – 6 inches | 7.5 – 15 cm | 2 points |
| 6 inches – 9 inches | 15 – 23 cm | 3 points |
| Greater than 9 inches | > 23 cm | 4 points |
| Hole / tear (regardless of size) | usually at any size | mostly 4 points |
Two basic rules discipline the scoring. The first is the maximum penalty per yard: the points accumulated within one linear yard (≈0.91 m) cannot exceed 4; even if there are several overlapping defects in the same area, that yard is recorded with at most 4 points. The second is that a continuous defect (selvedge-to-selvedge streak, a running line) is generally treated separately and, in some buyer protocols, can on its own cause the lot to be rejected. Since these nuances vary by buyer standard, it is important to clarify the acceptance protocol before ordering; let's clarify these thresholds together with KARCEM.
How many points per 100 yards are acceptable?
The normalisation formula makes the raw score independent of the fabric's actual size. The commonly used calculation is as follows:
- Sum the total points from all inspected defects.
- Calculate the unit area: inspected length (yards) × fabric width (inches).
- Find the points per 100 square yards: (Total points × 36 × 100) ÷ (inspected yards × width inches). The 36 here is the inch equivalent of a yard.
Example logic: if 35 points are accumulated on a roll 120 yards long and 60 inches wide, the normalised score ≈ (35 × 3600) ÷ (120 × 60) = 17.5 points/100 sq yd. If this value is below the contractual threshold, the roll is accepted. In the metric system the same logic is set up with points per square metre (typically a reference of ~23-30 points/100 sq m); when switching between the two systems, attention must be paid to unit consistency.
The point to emphasise is that the acceptance threshold lives in the contract, not in the product. The defect density that an underwear single jersey can tolerate differs from that of an interlock fabric to be used for outerwear. For this reason, rather than committing to a specific acceptance figure, the correct approach is to define the threshold together according to the end use and the buyer's quality manual.
How much should the GSM and width tolerances be?
While the 4-point system measures visual defects, GSM and width tolerances safeguard the fabric's dimensional and mass conformity. Even if a fabric contains no visual defects at all, being well below the target GSM or having a narrow width may be unacceptable for B2B purchasing - because this means both cost (cutting yield, metreage per kg) and final product performance.
GSM (GSM), as detailed in the GSM guide, is measured in grams per square metre and verified by weighing samples taken with a standard sample cutter (for example a 100 cm² round cutter). Width measurement is taken between the selvedges as tubular/open width; in knitted fabric, spirality and tension require the measurement to be taken in the relaxed state.
| Parameter | Measurement/unit | Typical tolerance (industry norm) |
|---|---|---|
| GSM | g/m² | usually target ± 5% |
| Width | cm (in relaxed state) | typically ± 1-2 cm |
| Shrinkage / dimensional stability | % (after washing) | by contract according to end use (see shrinkage test) |
| Colour difference (lab-dip → production) | ΔE / CMC(2:1) | according to approval standard (KARCEM: ΔE<1) |
| Metreage / roll length | m | determined by contract |
It is important to understand why tolerance bands are so fabric-specific: in a high-GSM interlock rib (2x2) knit, ±5% means a wide range in absolute grams, whereas in a fine single jersey the same percentage corresponds to a very narrow band. Similarly, in fabrics containing elastane, width is extremely sensitive to tension history; for this reason, the compacting/relaxation conditions are standardised before measurement.
How does the inspection flow work in practice?
A well-designed inspection process follows these steps:
- Sampling plan: rather than the whole lot, a representative percentage (according to the buyer protocol) is inspected. Statistical assurance is targeted, not a zero-defect guarantee.
- Visual scoring: the roll is passed at a constant speed across an inspection table with controlled lighting; each defect is marked, its size measured and scored according to the 4-point thresholds.
- Dimensional measurement: in the relaxed state, GSM (sample cutter + precision balance) and width are measured at several points; beginning–middle–end differences are recorded.
- Colour control: the colour difference of the production lot is measured against the lab-dip approval; at KARCEM the target is ΔE<1. (Detail: colour fastness and ΔE.)
- Calculation and decision: the normalised score and tolerance results are compared with the contract thresholds; the decision is given as pass/conditional acceptance/reject.
- Documentation: the defect map, measurement values and decision report are sent together with the shipment; traceability is ensured.
Conditional acceptance is an important intermediate decision in B2B practice: if the threshold is slightly exceeded, the parties may agree on a price adjustment, marking of the defective areas (string/sticker) or partial return. For this reason inspection is not merely a "pass/fail" button but a data layer that feeds the commercial negotiation.
The advantage of a vetted contract network appears precisely here: when in-house knitting and the contracted dyeing, finishing and inspection are coordinated under one point of contact, once a defect is detected the root cause (is it the knitting needle, the dye bath, the stenter setting?) can be quickly traced back and corrected. This feedback loop is detailed on the coordinated contract network advantage page.
What is done in the event of tolerance overrun and rejection?
An overrun does not always mean rejection of the entire lot. In most cases the defects are concentrated in certain rolls; once these are segregated, the remainder may stay within the threshold. GSM deviation is related to production parameters (for example compacting/sanforising setting, knitting density) and can be corrected in subsequent lots; width deviation is managed by the stenter width setting.
The permanent solution is to prevent the defect from occurring before catching it in inspection. For this, the acceptance criteria (sample approval, quality manual, target GSM/width and points threshold) must be fixed in writing at the order stage. Measurable parameters, rather than a vague "make it good quality" expectation, protect both the manufacturer and the buyer.
Frequently asked questions
What exactly does the four-point inspection system measure and which standard is it based on?
The four-point system (ASTM D5430 / four-point) is the industry's most widely used method, grading each visual defect in the fabric from 1 to 4 points according to its size. It measures visual integrity; it does not replace laboratory tests such as colorfastness, shrinkage or pilling, but complements them. By normalizing the total points to a unit area, it reduces the lot's pass/fail decision to a single objective, repeatable number.
How many points are assigned to a defect according to its size?
Points are assigned according to the defect's longest dimension: 3 inches (≈7.5 cm) and under scores 1 point, 3-6 inches scores 2 points, 6-9 inches scores 3 points, and over 9 inches scores 4 points. Holes mostly receive the highest score (4) regardless of size. Direction does not change the score; only length matters. The maximum points that can be assigned to a single defect within one linear yard is capped at 4.
How many points per 100 square yards are acceptable?
The threshold frequently referenced in the industry falls in the range of 20-40 points per 100 square yards; on the metric side, roughly 23-30 points/100 m² is taken as reference. However, there is no single universal pass figure: the actual acceptance limit is set by contract according to the fabric type, end use and buyer standard. The acceptance threshold lives in the contract, not in the product.
How is the normalized point score calculated?
First, the total points of all defects are summed. Then the formula (Total points × 36 × 100) ÷ (inspected yards × width in inches) is applied; 36 is the inch equivalent of a yard. Example: for a length of 120 yards, a width of 60 inches and 35 total points, the normalized score ≈ (35 × 3600) ÷ (120 × 60) = 17.5 points/100 yd². If this value is below the contractual threshold, the roll is accepted.
What is the acceptable tolerance band for weight and width?
As an industry norm, ±5% of the target value is taken as reference for weight and typically a ±1-2 cm band for width. These values vary according to the fabric type, weight class and finishing process and should be fixed by contract. Weight is determined by weighing a standard sample cut (e.g. a 100 cm² round cutter), while width is measured in the relaxed state of the knit fabric, between the selvedges.
What is done when a tolerance or point threshold is exceeded?
Exceeding a limit does not always mean rejection of the entire lot. The options are: segregating the affected rolls, negotiating conditional acceptance (price adjustment, marking the defective area or partial return), reprocessing, or rejecting the lot. Weight deviation is corrected with compacting/sanforizing and knit density, while width deviation is corrected with the stenter width setting. The correct approach is to base the decision on inspection data and the acceptance criteria in the contract.