Kit Verification and BOM Accuracy

A kit is the collection of material for one build, gathered before the build starts and verified against the bill of materials. Done well, it moves the verification away from the machine, where every mistake costs production time, to a bench where a discrepancy can be resolved calmly. Done badly, it becomes a box of parts with an assumption attached, and the assumption is what the line then builds to.

What a Kit Has to Guarantee

A kit has to guarantee three things: that every part on the bill of materials is present in the right quantity, that each part is the correct approved item rather than a similar one, and that the documentation that travels with the build matches the revision being built. Any of the three can fail, and each failure has a different symptom: a shortage stops the line, a wrong part produces a defect, and a wrong revision produces a product that does not match its specification.

The kit is also the point at which a shortage becomes visible. Finding out that a part is missing on the bench allows time for a decision, while finding out at the machine stops production. That difference alone is often enough to justify the cost of kitting, before any quality benefit is counted. Work instruction practice should state where the kit is verified and by whom.

Building the Kit

The kit is built from the bill of materials and the work order, and it should be assembled in a defined area with the actual material rather than from stock records. Each line is picked, counted and placed in a labelled position, and the picker records the lot for the parts that require traceability. Where the kit is built from a pick list generated by the system, the list should show the internal part number rather than a description, because descriptions are not unique.

The physical arrangement matters as much as the content. Trays with a position for each line item, labelled with the part number and the quantity, allow a missing or extra item to be seen immediately. Where the kit is loose in a box, verification becomes a search. Incoming material should already have been verified, so the kit check is about presence and identity rather than quality.

Scan Verification

Scanning each item against the pick list is the most reliable verification method available. The scan confirms the identity of the part, and where the system holds the lot, it also creates the traceability record. The rule that makes it effective is a negative one: the system must reject a mismatch, and the operator must not be able to proceed without resolving it or recording an authorised exception.

Where scanning is not available, a two-person verification with a signature has proved reliable for high-value or easily confused parts. The second person reads the label against the list, which catches the error that the first person made because they were reading what they expected rather than what was there. Documenting which parts require the second check is more practical than applying it to everything.

Handling Discrepancies

Discrepancies should be resolved before the kit is released, and the resolution should be recorded. A missing item is either picked and added, or the build proceeds without it under a documented shortage plan. An extra item is removed and the cause investigated, because an extra part often indicates a picking error elsewhere in the same kit. A wrong item is replaced, and the incorrect part is returned with a note rather than quietly put back on the shelf.

The record matters because discrepancies are a symptom. A kit that consistently has one or two errors may be built from a bill of materials that is ambiguous, from a pick list that is hard to read or from material that is stored in a confusing way. Counting discrepancies per kit and reviewing the causes turns individual errors into a process improvement. Document control is where the bill of materials accuracy starts.

Bill of Materials Accuracy

The bill of materials is the source of everything downstream, and an error in it propagates into the kit, the program and the documentation. Common faults include a missing alternate, an unapproved substitution that was never recorded, a quantity that does not match the assembly drawing and a part number that refers to an obsolete item. Each of these should be caught before the build, not during it.

The accuracy of the bill of materials should be verified when it is released, ideally by building a first article from it rather than by reading it. Cross-checking the bill against the assembly drawing and the placement program catches the majority of discrepancies, because a part that appears in one and not the other is visible immediately. Where the checks are automated, they take seconds and should run on every revision.

Partial Kits and Shortages

Where the full kit cannot be assembled, the shortage should be defined rather than absorbed. A partial kit that is released to the line will be discovered at the station, and the decision about a substitute will then be made under pressure. Planning the shortage in advance allows the substitution to be approved, the documentation to be updated and the traceability to be recorded before the build starts.

The partial kit should be marked as such, with the missing items listed and the plan for each. Where the plan is to add the part later, the work instruction should say so and the traveller should carry a reminder, because a part added after test is a part that was not tested. Quality checks should include confirmation that all deferred items were added.

Records and Audits

The kit record should show what was issued, by whom, when and against which work order, with the lot information for traceable parts. The record is what allows a question about a specific build to be answered, and it is what supports the traceability chain from component to finished unit. Where the record is optional, it will be missing exactly when it is needed.

An audit of the kitting process should sample a kit and verify it independently, checking the content, the labelling and the record. Where discrepancies are found, the cause should be traced to the pick list, the storage or the bill of materials rather than being treated as an operator error. The audit’s value is in the fixes it triggers.

Improving Kit Accuracy

Accuracy improves when the kit is easy to build correctly. Storing similar parts in clearly separated locations, using colour or position to distinguish values that are easy to confuse and printing pick lists in a legible sequence all reduce errors without adding a control step. The same principle applies to the trays that hold the kit, since a tray with an obvious empty position makes a missing item apparent.

Measuring the kit accuracy rate, and the number of discrepancies per hundred lines, provides the feedback that keeps the process improving. Where the rate is high, the causes are usually in the material storage or the documentation rather than in the people, and the improvements are correspondingly durable. A kit process that reaches a high accuracy rate reduces the pressure on the machine operator and shortens changeover.

FAQ

Does every build need a kit? Every build with more than a handful of unique parts benefits. The larger and more varied the material, the greater the return.

Who should verify the kit? Somebody other than the person who picked it, using a scan or a second read. Self-verification catches fewer errors.

What should happen to a wrong part found in a kit? Replace it and record it. A wrong part usually indicates a picking or storage problem that affects other kits too.

How is kit accuracy measured? As the number of discrepancies per build or per hundred lines picked, with the causes categorised so that the improvements can be targeted.