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DropGear

Study · published 27 August 2026 · updated 29 August 2026 · DropGear Oy Ab

Attribute data quality of aftermarket parts in Finland

DropGear compared 52,231 aftermarket articles against the reference values of the same OE number. 20.3% of the articles deviated from the reference value in at least one measured attribute and 33.9% lacked sufficient attribute data for comparison. 45.8% matched the reference value. The comparison covers dimensional, mass and count-based attributes; classification attributes are not included, so the share of deviating articles is a lower bound.

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52,231
articles compared

across 4,494 OE numbers

20.3%
deviate from the OE reference value

in at least one attribute

33.9%
insufficient attribute data

no comparison possible

45.8%
match the OE reference value

23,908 articles

Why this is measured

The error is structural, not human

Wrong-part orders in the parts trade are not mainly caused by mistakes at the counter, but by article data that contradicts itself. The same part can appear in different supplier catalogues with a different weight, a different thickness and a different diameter. When the correct part is chosen from catalogue data alone, the error is structural rather than human.
Method. Every aftermarket article is linked to the original OE number, and its reported attributes (weight, dimensions, diameters, thicknesses) are compared against the reference value of that OE number. The reference value is weighted towards the original manufacturer’s attribute data: values reported by aftermarket suppliers are observations to be compared, not votes. An article is flagged as deviating if at least one attribute differs from the reference value. The comparison is run against a digital twin of the Finnish vehicle parc, so every article is anchored to a real vehicle population rather than to catalogue data alone.
The comparison covers numeric dimensional, mass and count-based attributes: 202 attributes in this dataset, of which 161 are millimetre dimensions, 5 kilogram masses and 34 count-based attributes such as number of teeth and number of holes. Classification attributes, such as connector type, are not part of the comparison, so the share of deviating articles remains a lower bound in that respect.
An article means one supplier product number for one OE number; the same physical part therefore appears as a separate article for every supplier that lists it. Tables 1 and 2 describe sets of different scope: table 1 covers 52,231 articles across 4,494 OE numbers for which the platform has compiled the full list of aftermarket options, while table 2 is based on a wider validation run of 57,341 articles flagged as deviating across 3,289 OE numbers. The sets overlap on 782 OE numbers, and the 10,623 deviating articles of table 1 are contained in full in the table 2 dataset.

Validation status of articles

Table 1. Validation status, 52,231 articles across 4,494 OE numbers

StatusArticlesShare
Matches OE reference value23,90845.8%
Deviates from OE reference value in at least one attribute10,62320.3%
Insufficient attribute data for comparison17,70033.9%
Total52,231100.0%

Supplier names and article numbers are not published.

Most frequently deviating attributes

Table 2. Deviations by attribute (extended validation dataset, 3,289 OE numbers), 81,282 attribute-level deviations

AttributeDeviationsShare
Weight [kg]15,82219.5%
Width [mm]7,3209.0%
Height [mm]7,0128.6%
Length [mm]5,3546.6%
Thickness [mm]3,5114.3%
Outer Diameter [mm]3,2374.0%
Height 1 [mm]3,1453.9%
Net weight [kg]2,8583.5%
Height 2 [mm]2,7703.4%
Inner Diameter [mm]2,4903.1%

57,341 articles were flagged as deviating. A single article can deviate in several attributes at once, giving 81,282 attribute-level deviations in total (a mean of 1.42 per article, up to 9). The ten most frequent attributes account for 53,519 of them, or 65.8%.

Which attributes are compared

Table 3. Attribute coverage of the comparison, 202 attributes

Attribute classAttributesDeviationsShare
Linear dimensions [mm]16153,27665.5%
Mass [kg]520,07424.7%
Count-based (quantities)347,1568.8%
Other (OE criteria and reference fields)27761.0%
Total20281,282100.0%

The comparison covers dimensional, mass and count-based quantities. For timing belt, timing chain and pulley parts, for instance, the number of teeth and the number of chain links are compared in addition to width, diameter and mass. Classification attributes, such as connector type, are not included. The full attribute list is available as a CSV download.

Magnitude of deviation

Table 4. Deviation relative to the OE reference value

MetricValue
Numerically comparable attribute values80,611
Median deviation from the reference value20.0%
Share deviating by more than 10%70.2%
Share deviating by more than 50%28.7%

There were 81,282 attribute-level deviations in total. Of those, 671 are reported in a non-numeric form, so no relative difference can be calculated, which leaves 80,611 deviations in the magnitude comparison. The median and the shares are calculated from that set.

How many options the correct part is chosen from

Table 5. Aftermarket options per OE number, 4,494 OE numbers

OptionsOE numbersShare
1 option1,84441.0%
2–391220.3%
4–1090520.1%
11–5059113.2%
over 502425.4%
Total4,494100.0%

Median 2 options, mean 11.6, up to 448 options for a single OE number.

Frequently asked questions

Questions about the study

What does the reference value mean?

The reference value is the value considered correct for an attribute of a given OE number. It is weighted towards the original manufacturer’s attribute data, with values reported by aftermarket suppliers acting as supporting evidence. It is not a majority vote among suppliers: among the deviating articles, the reference value falls entirely outside the range of supplier-reported values in 67.0% of cases.

Is the number of teeth included in the comparison?

Yes, as of this version. The comparison also covers count-based attributes: 34 attributes, including number of teeth, number of holes and bolts, and the number of parts in a kit. They account for 7,156 attribute-level deviations, of which 1,765 relate to tooth counts. Classification attributes, such as connector type, are still not compared, so the share of deviating articles remains a lower bound in that respect.

Why do nearly half of the articles have insufficient data?

A comparison requires a comparable attribute value to have been reported for the article. For some articles no attributes are reported at all, or they are reported in different units, which makes a reliable comparison impossible.

Are supplier-specific results published?

No. Results are reported at aggregate level only, without supplier names or article numbers.

What is this data used for?

DropGear’s PartsFinder365 system uses the validation in its own parts search and range optimisation: an article whose attributes deviate from the OE reference value can be surfaced before an order is placed, which reduces the risk of wrong-part orders. The aggregate figures are published to make the scale of a problem shared by the whole industry visible: suppliers can target product data corrections at the most frequently deviating attributes, and buyers can see when catalogue data alone is not enough to pick the correct part. The sample is updated quarterly, so progress can be tracked against the same metrics.

Does the dataset contain personal data?

No. Vehicle VINs, registration numbers, user identifiers and customer company identifiers are removed before aggregation. All published figures are aggregate-level figures.

May the figures be used?

Yes. The dataset is available under the CC BY 4.0 licence with attribution to DropGear Oy Ab / PartsFinder365.

Validation is part of every PartsFinder365 search

An article whose attributes deviate from the OE reference value is surfaced before the order is placed. See how the platform uses this data in parts search and range optimisation.

Explore PartsFinder365