Understanding the NGK Spark plug codes:
The combination of letters and numbers assigned for every NGK spark plug is not only the type designation, it is a logical formula which contains the important details for the function of the spark plug.
With this spark plug formula NGK has standardised its entire assortment and made the specific characteristics of the respective spark plug clearly recognisable.
The typical designation is as follows:
- The first group of letters (either 3 or 4) before the heat rating number indicates the thread diameter, the spanner size needed for the hexagon nut and the design. (eg BKR5EIX is a the smaller hex nut and BPR5EIX is the larger hex nut, apart from that they are identical plugs).
- The first number in the sequence indicates the heat rating. (eg BKR5EIX is a 5 heat range plug. High numbers are progressively Colder, lower numbers are progressively Hotter)
- The next letter identifies the thread length. (eg BKR5EIX)
- The following letter contains data about special spark plug construction features. (eg BKR5EIX means the plug is an Iridium type)
- And a possible final number may codify special electrode distances. (eg BKR5EIX-11 means the plug is gapped to 1.1mm out of the box)
- This is a great link to a lot more info from NGK about their plugs LINK
QUICK REFERENCE FOR COMMON TRIALS BIKES:
Bultaco - NGK B5HS
Gas Gas JT/JTR/JTX/Contact/Pro/Racing/Raga/Factory 95-17, Ossa 11-15, Scorpa ST/Twenty 11-17, Sherco 99-17 - BPR5ES or BKR5E
Montesa 4RT - CR6EH-9
Montesa 314-315 94-04 - BR6ES
Jotagas 12-17, Vertigo Combat 16-17, TRS 16-17 - BPRMR4A and BPMR6A