The ACDelco Spark Plug Identification Table
Prefix and suffix letters are used to identify a specific type plus the numbers relate to thread size and heat range. For example, the R45TS spark plug shown is:
- R = Resistor
- 4 = 14 mm Thread
- 5 = Heat Range
- T = Taper Seat
- S = Extended Tip
| Identification Code | Description |
|---|---|
| B | Series Gap |
| C | Commercial |
| CS | Chain Saw |
| F | Fine Line 14 mm 5/8" Hex |
| M | Marine |
| LM | Lawn Mower type |
| R | Resistor |
| S | Shielded (5/8-24 thread) |
| V | Surface Gap |
| Prefixes are sometimes combined e.g., VB, CR | |
Numbering
- 1st number denotes THREAD SIZE
- 2nd number denotes HEAT RANGE
In the early 1990s, an all-numeric, identification code was developed to ensure that the proper spark plug would be selected for replacement in specific engine applications. The numeric code does not in any way correspond to the heat range of the spark plug. Therefore, selection of a spark plug with a different code number is not recommended. The heat ranges may be drastically different between two different plugs, and engine damage or poor performance may result. See your local installer or retailer for details.
The prefix “41” stands for the manufacturer’s product line (e.g., 41 = spark plug)
Numbers after the prefix indicate the type of spark plug and also the specific application:
- 100 – 199 = Iridium
- 600 – 699 = Resistor
- 800 – 999 = Double Platinum
| Identification Code | Description |
|---|---|
| A | Cap Gap |
| C | Copper Core Center Electrode |
| C | Colder Version of M44 Plub |
| E | Special Design Electrode Extended Tip |
| F | 1/2" (12.7 mm) reach |
| FF | 1/2" (12.7 mm) reach, fully threaded |
| G | Pin Gap (cold-running) |
| I | Iridium Center Electrode |
| J | Boot Release Agent, Anti-Seize Compound |
| K | Special Design |
| L |
Long Reach 7/16" (11.1 mm) reach, (14 mm) thread 3/4" (19 mm) reach, (18 mm) thread 3/4" (19 mm) reach, (14 mm) thread (fineline) |
| LT | Long reach, .715" (18.16 mm), Tapered Seat |
| M | Special Design Electrode |
| N | 3/4" (19 mm) reach, 3/8" (9.5 mm) thread length |
| R | Resistor (Sport Vehicle Plugs) |
| S | Extended Tip |
| S |
7/8" (22.3 mm) Moderate Long Reach 23/32" (18.25 mm) |
| T | Tapered Seat Shell Design |
| TS | Tapered Seat with extended tip |
| XL | Extra Long Reach, 3/4" (19 mm) fully threaded |
| Y | 3-Prong Cloverleaf Electrode |
| Z | Special Gap (usually denotes wide gap) |
| 5 | .050" (1.3 mm) gap |
| 6 | .060" (1.5 mm) gap |
| 8 | .080" (2 mm) gap |
| 100 | Iridium |
| 600 | Resistor Type |
| 800 | Platinum Type |
| 900 | Double Platinum Type |
| Suffixes are combined to form such AC suffix designations as FG, XLS, TS, FFM, TSX, SZ, etc. | |
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