First off the ngk codes...

How to decode NGK plug numbers:

A: 18mm thread C: Hex size 5/8"
B: 14mm thread K: Hex size 5/8 projected tip (ISO)
C: 10mm thread M: Compact
D: 12mm thread P: Projected insulator
J: 12mm thread R: Resistor
U: Surface or semi-surface discharge
Z: Inductive resistor

Thread reach:

E: 19mm
F: Tapered Seat

Heat Range H: 12.7mm (1/2")

L: 11.2mm (7/16")
None: 18mm thread = 12mm reach

4mm thread = 9.5mm (3/8") reach

Firing End Construction:

A: Special Design
P: Premium Platinum
B: Special design for
Q: 4 ground electrode

Honda CVCC R: Special ground electrode

C: Low angle ground
S: Standard 2.6mm
electrode center electrode

B CPR 6 E S - 11
G: Fine wire nickel alloy
T: 3 ground electrode

center electrode U: Semi surface discharge

Wide Gap: GV: Gold Palladium center
V: Fine wire gold palladium
8: 0.8mm (0.032") electrode, special type center electrode
9: 0.9mm (0.036") of V-type, racing use
10: 1.0mm (0.040")
11: 1.1mm (0.044")
13: 1.3mm (0.050") for Toyota, BMW
14: 1.4mm (0.055")
15: 1.5mm (0.060")
20: 2.1mm (0.080") 
VX: High performance platinum
H: Partial thread
W: Tungsten electrode
K: 2 ground electrodes
X: Booster Gap
Y: V-grooved center electrode
L: Half heat range
Z: Thick 2.9mm center electrode
LM: Compact type for lawn mower
M: 2 ground electrodes for Mazda rotary
N: Special side electrode

‘S’ TYPE (e.g. BP6ES)

NGK standard spark plugs with copper cored centre electrodes for wide heat range. Copper’s superior heat conductivity dissipates the heat of combustion away from the firing end, preventing hot spots that can lead to pre-ignition.

Copper cored electrodes also mean that longer insulator noses can be used to protect against fouling.

‘G’ TYPE (e.g. B10EG)

These plugs feature a smaller diameter centre electrode tip made of conventional nickel alloy. The smaller diameter centre electrode means the voltage required to produce a spark is reduced. However as the tip is made of conventional nickel alloy the service life is reduced and these plugs are best used in applications where plugs are frequently changed.

‘V’ TYPE (e.g. B10EV)

The centre electrode of this type is made of gold palladium alloy and is even smaller in diameter than the G type at 1.0mm and has therefore an even lower voltage requirement. Now mostly superseded by ‘VX’ types.

‘GV’ TYPE (e.g. B9EGV)

These plugs have a centre electrode of precious metal similar to the V range. In addition the insulator nose is an improved design to allow better gas flow around the firing end. The ground electrode is shorter and stronger, making the GV range more suited for racing applications.

‘VX’ TYPE (e.g. B8EVX)

These plugs have an even smaller centre electrode (0.8mm) than the V types and this is made of platinum. This combined with a taper cut ground electrode means an even lower required voltage than the V types.

The result is better ignitability along with improved starting, idle stability and anti-fouling performance.

‘IX’ TYPE (e.g. BR8EIX)

Similar in design to the Platinum VX spark plug, the use of the precious metal Iridium allows us to manufacture a spark plug with an even smaller diameter centre electrode (0.6mm) without compromising durability. This extremely small Iridium tip centre electrode concentrates the available electrical energy and combined with the taper cut ground electrode provides the best performance in terms of starting, idling and especially throttle response.