Attribute Schema Library
Attribute schemaautomotive aftermarket

Spark Plug Attributes

A spark plug threads into the cylinder head, seals the combustion chamber, and fires the coil's discharge across a fixed electrode gap. Aftermarket distributors sell them to jobbers, independent shops, fleets, and DIY retail — almost always against a vehicle application, not against a spec sheet.

The part number is the spec. NGK's BR9EG, Champion's RC12YC, and Denso's IK20 each encode thread, reach, heat range, and firing-end design in a different proprietary scheme, so nothing cross-references without a decode table.

And heat range is brand-relative and inverted: on NGK and Denso a higher number is colder; on Champion, Autolite, and Bosch a higher number is hotter. Pooled into one column across brands, it stops being a filter. Meanwhile torque, seat type, and OE gap sit in installation PDFs, while the item feed carries ACES fitment — which answers "does it fit," never "what is it."

Core

Every SKU needs these. Without them the record is not a product, it is a row.

Manufacturer Part Number (MPN)
identifier
NGK 3230 (plug code BR9EG)

The plug is ordered by MPN, and the MPN encodes the spec. Stock number and catalog number often differ from the printed plug code.

Thread Size
enum · mm x pitch
M14 x 1.25

First hard filter. Wrong thread does not start. ISO 28741 metric sizes only: M8, M10x1.0, M12x1.25, M14x1.25, M18x1.5.

Reach (Thread Reach)
number · mm
19.0 mm (0.750 in)

Length of threaded shell. Too short leaves carbon on exposed threads; too long lets the piston strike the plug. Not implied by thread size.

Seat Type
enum
Gasket (flat), crush washer included

Gasket (flat) seals via a crush washer; taper (conical) seals metal-to-metal with no washer. Determines torque and whether a washer ships.

Hex Size
enum · mm / in
15.9 mm (5/8 in)

Decides which plug socket the tech needs. 5/8 in and 13/16 in dominate; compact ISO heads use 14 mm and 16 mm.

Terminal Type
enum
Removable nut

Solid (fixed nut), removable nut, or threaded stud. Determines whether the coil boot or plug wire terminal will seat.

Resistor
boolean
Yes — 5 kΩ

Resistor plugs suppress RFI (~5 kΩ). Non-resistor plugs in a modern ECU vehicle throw misfire codes and interfere with electronics.

Installed Height / Overall Length
number · mm
50.5 mm (1.99 in)

Clearance check against coil-on-plug boots, valve covers, and plug wells. Reach alone does not tell you if the coil seats.

GTIN / UPC
identifier
UPC-A (12-digit); GTIN-14 for the 4-pack

Required for marketplace listing and WD receiving. Single plug and multi-pack carry different GTINs.

Differentiating

What buyers actually compare on. This is where catalogs win or lose the filter.

Center Electrode Tip Material
enum
Iridium, 0.6 mm fine wire

Copper/nickel, platinum, iridium, or ruthenium. Drives price tier, service life, and whether the plug can be re-gapped at all.

Ground Electrode Tip Material
enum
Platinum pad

Separate from the center tip. A 'double platinum' plug is platinum on both; 'laser iridium' is often iridium center with a platinum ground pad.

Center Electrode Core Material
enum
Copper

Copper core conducts heat out of the tip and widens the effective heat range. Distinct from the tip material buyers shop on.

Heat Range
number
9 (NGK scale)

Rate the tip sheds heat to the head. Too hot pre-ignites; too cold fouls. Meaningless without the brand's scale — see Heat Range Scale.

Pre-Gap Size
number · mm / in
0.6 mm (0.024 in)

The gap as shipped from the factory. On fine-wire plugs this is set precisely and is not always the OE spec gap.

OE-Recommended Gap
number · mm / in
1.1 mm (0.044 in)

The gap the vehicle actually calls for. Separate field from pre-gap; the two disagree often enough that buyers need both.

Ground Electrode Configuration
enum
Single ground, J-gap

Single J-gap, multi-ground (2-4), surface gap, or projected. Affects fitment in swirl chambers and the plug's fouling behavior.

Compliance & identifiers

Standards, regulatory data, and the identifiers channels reject you for missing.

ACES Fitment Coverage
identifier
ACES 4.2 XML, VCdb BaseVehicleID + EngineBase

Vehicle applications as VCdb BaseVehicleID plus engine qualifiers. Without it the part cannot appear in any year/make/model part finder.

Country of Origin
text
JP

Required on PIES item feeds and for customs, duty, and USMCA claims. Plug lines are commonly split across JP, DE, MX, and CN plants.

The fields that aren't in the schema at all

What most spark plugs catalogs are missing.

The table above is the schema most catalogs already have. These are the attributes that usually aren't in it — each one surfaced by a signal from the live market rather than by an audit of what's already there. This is what Anglera's Schema Foundry does on a real catalog, in this category.

Competitor signal
+ Heat Range Scale Direction

NGK publishes a heat range conversion chart precisely because the scales are inverted. Distributor filter rails still show a bare 'Heat Range: 9' with no brand scale attached.

A cross-brand heat range filter silently mixes hot and cold plugs. Buyer moves from a Champion 8 to an NGK 8 expecting similar and gets the opposite end.

Review signal
+ Gappable / Fine-Wire Flag

Iridium plugs ship pre-gapped under a protective sheath with a 0.4-0.6 mm center tip that fractures under a gapping tool. Catalogs carry a Gap field but none saying if the gap may be touched.

Customer snaps the iridium tip with a coin-style gapper and returns the plug as defective. The return is warranty-coded and the counter has no data to push back with.

Supplier signal
+ Installation Torque

Every major brand publishes torque tables by thread size, seat type, and head material, but the value stays in the installation PDF and never reaches the SKU record.

Torquing a taper-seat plug at gasket-seat values cracks an aluminum head; under-torqued plugs run hot and blow out. Neither is the plug's fault, both land as claims.

Marketplace signal
+ OE-Recommended Gap (separate from Pre-Gap)

RockAuto exposes Pre-Gap and OE-Recommended Gap as two distinct fields and they routinely disagree — a plug pre-gapped at 0.041 in against an OE spec of 0.043 in.

One ambiguous 'Gap' column leaves the installer guessing whether to adjust. Wrong gap means rough idle, misfire codes, and a return on a part that was correct.

Search signal
+ Recommended Service Interval

Buyers shop plugs by replacement life — copper at roughly 20-30k miles versus iridium and platinum at long-life intervals — and search that way. Almost no distributor rail offers it as a facet.

Loses the premium upsell path. The long-life plug that justifies its price has nothing in the record to justify it with, so the search defaults to cheapest.

How Schema Foundry finds these

Messy in, governed out.

The same value, spelled every way automotive aftermarket suppliers spell it. A filter only works once they agree.

Thread Size
14mmM14M14x1.25M14 - 1.2514 x 1.250.551 in
M14 x 1.25

One supplier sends thread diameter in inches, another sends diameter and pitch in one string. Neither filters until pitch is split out.

Seat Type
FlatGasketGasket SeatWasherTaperConical
Gasket (flat) | Taper (conical)

This field sets the torque spec. Gasket and taper at M14 in aluminum differ by roughly 15 Nm — enough to crack a head.

Electrode Gap
0.0440.044".044 in44 thou1.1mm1,1 mm
1.1 mm (0.044 in)

European suppliers send comma decimals; US suppliers send bare thousandths. '1,1' parses as 11 in most import jobs.

Electrode Material
Iridium IXLaser IridiumDouble IridiumIrIridium/PlatinumDouble Platinum
Center tip: Iridium | Ground tip: Platinum

Brand marketing names compress a two-field truth into one string. 'Laser Iridium' is not the same construction as 'Double Iridium'.

What buyers ask

Every one of these should be answerable from the attributes above. If it isn't, that's a gap.

  • Will this fit my 2016 Silverado 5.3L?
  • Is the NGK 6 hotter or colder than the Champion 8 I pulled out?
  • Do I need to gap these iridiums or are they good out of the box?
  • What do I torque these to on an aluminum head?
  • Is this a resistor plug? My ECU throws misfires without one.
  • Does this take a 5/8 or a 13/16 socket?
  • Is the reach the same as the plug that came out?
  • How many miles do these last before I'm back in there?

What channels require

The same SKU, different mandatory fields per destination.

Amazon (Automotive / Part Finder)
ACES fitment file (VCdb)GTIN/UPCMPNBrandPCdb part terminologyImages
eBay Motors (Parts Compatibility)
ACES-derived compatibilityMPNBrandInterchange / OE cross-referenceGTIN
WD feeds (Keystone, LKQ, Turn 14, Nexpart)
PIES item segmentPAdb attributesBrand Table AAIAIDGTINCountry of OriginPackage UOM and quantity
Distributor's own filter rail
Thread sizeReachSeat typeHex sizeHeat range + scaleElectrode tip materials

Spark Plugs data, in practice

Why can't I filter heat range across brands?

Because the scales run in opposite directions. On NGK, Denso, and Pulstar, a higher number means a colder plug. On Champion, Autolite, and Bosch, a higher number means a hotter plug. The numbers are also not calibrated to each other — a Champion 10 is not an NGK 10 on any scale. NGK publishes a heat range conversion chart for exactly this reason. A single pooled 'Heat Range' column is worse than no column, because it returns confidently wrong results. Carry the number and the scale as separate fields, or store a normalized heat index alongside the brand value and filter on that.

What's the difference between pre-gap and OE-recommended gap?

Pre-gap is the gap set at the factory and protected in the packaging. OE-recommended gap is what the vehicle's ignition system actually calls for. They often match, but not always — a plug can ship pre-gapped at 0.041 in against an OE spec of 0.043 in. Distributors that carry only one 'Gap' field force the installer to guess whether adjustment is needed. This matters most on fine-wire plugs: an iridium center electrode is 0.4-0.6 mm and fractures if a gapping tool touches it, so the answer to 'should I adjust this' has to come from the record, not the bench.

Do I really need ACES and PIES if I have good attributes?

They answer different questions. ACES carries fitment — which vehicles the plug applies to, expressed as VCdb BaseVehicleIDs with engine qualifiers. PIES carries the item: identifiers, packaging, country of origin, and PAdb attributes. Without ACES, the part cannot appear in any year/make/model part finder, on your site or on Amazon and eBay Motors. Without PIES attributes, it appears in the finder but has nothing to compare on. Most spark plug catalogs are strong on ACES and thin on PAdb, which is why they answer 'does it fit' but not 'which one should I buy.'

Why does seat type matter so much for a data field?

Because it sets the torque spec, and the spread is wide enough to break parts. A 14 mm gasket-seat plug in an aluminum head takes roughly 25-30 Nm — the torque crushes the washer to form the seal. The same head with a 14 mm taper-seat plug takes roughly 10-20 Nm, because it seals metal-to-metal by wedging. Torquing a taper seat to gasket-seat values is a leading cause of cracked aluminum heads. Seat type also determines whether a crush washer ships with the plug, which is its own source of counter returns.

More automotive aftermarket schemas

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