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Above is a diagram showing - Diameter, Reach and Hex measurements of a spark plug

Bantam Plug

Special purpose designs classified as Bantam because of their short overall length. They are required to meet space limitations of small engines with compact cowling or shrouds in certain equipment such as chain saws, lawn mowers, etc.

Marine

Marine spark plug's shell are double-dipped, zinc-chromate coated metal.

Racing

Racing spark plugs have been designed to withstand severe operating conditions, such as high combustion temperatures and increased pressures.

Screened Type

Fully screened spark plugs with steel jacket where very stringent demands are placed on suppression, for example in official vehicles. (Tanks etc)

Twin, Triple & Multi Electrode

Every time the plug sparks, minute particles of material are worn away from the electrodes. This phenomenon is called spark erosion. This continuous process over time increases the spark plug gap between the centre and the ground electrode. If the gap becomes too large, misfiring will occur.

In order to extend the service interval of vehicles, the service life of the spark plug must be increased. Some manufacturers are fitting multi electrode spark plugs as original equipment to achieve this. Multi electrode spark plugs can have two, three or four ground electrodes depending on the service life requirement of the manufacturer.

Do multi ground electrode spark plugs provide simultaneous sparks to each ground electrode every time the plug sparks? No. No matter how many ground electrodes the plug has, every time the spark plug fires, only one spark occurs between the centre electrode and the ground electrode which has the lowest required voltage or the least distance to travel between the centre and the ground electrode.

Standard Nkl Alloy

Standard electrodes with iron core used in most Spark Plugs

Copper Core

Copper core electrodes are good heat conductors and have high corrosion resistance.

Double Copper Core

Double copper core have centre electrodes and ground electrodes both covered, also copper is a good heat conductors and has high corrosion resistance.

Nickel Yttrium

Bosch spark plugs use nickel chromium ground electrode & Yttrium Centre electrode resulting in less electrode erosion & more protection against corrosion.

Yttrium

Bosch spark plugs use Yttrium Centre electrode resulting in less electrode erosion & more protection against corrosion.

Gold Palladium

For premium performance, a spark plug having a small diameter Gold Palladium centre electrode. The semi precious metal alloy makes it possible to provide extra performance design features resulting in faster, easier starts, fewer stalls and false starts, reducing fouling deposits and usually longer life. The spark plug design requires less ignition voltage than the conventional electrode type. The design also provides more clearance within the firing end of the spark plug, for better scavenging of fuel deposits and less fouling.

Iridium

Ngk use iridium spark plugs which offers extreme ignitability, improved throttle response and superior anti fouling. Fine Iridium tip ensures high durability and a consistently stable spark Iridium alloy has extremely high melting point, perfect for today’s high-tech, high-performance engines Trivalent Metal Plating - superior anti-corrosion and anti-seizing properties Outstanding acceleration, high fuel efficiency and durability Ultimate design, technology and performance.

Platinum

Nearly all spark plug manufacturers use platinum in one form or another on their long life or performance spark plugs. This is because of platinums high melting point, which makes it useful in two ways. On long life spark plugs a thin wafer of platinum is bonded at the firing point to the center electrode (and possibly ground electrode) solely so they do not wear as fast as a traditional plug. On a fine wire performance plug, the very tip of the center electrode is made of platinum so that the fine wire tip will last longer. Do not be fooled, all platinum plugs are not created equal. Platinum is a very expensive precious metal, a cheap platinum spark plug will not have much platinum in it, and therefore will not last as long as a expensive platinum spark plug. Some platinum plugs have only the center electrode tipped with platinum, while others have both the center and ground electrodes platinum tipped. (It is not suggested that platinum plugs be used on vehicles with nitrous injection, however, there have been no problems reported using iridium plugs with nitrous).

Double Platinum

Double Platinum have centre electrodes and ground electrodes both covered. Nearly all spark plug manufacturers use platinum in one form or another on their long life or performance spark plugs. This is because of platinums high melting point, which makes it useful in two ways. On long life spark plugs a thin wafer of platinum is bonded at the firing point to the center electrode (and possibly ground electrode) solely so they do not wear as fast as a traditional plug. On a fine wire performance plug, the very tip of the center electrode is made of platinum so that the fine wire tip will last longer. Do not be fooled, all platinum plugs are not created equal. Platinum is a very expensive precious metal, a cheap platinum spark plug will not have much platinum in it, and therefore will not last as long as a expensive platinum spark plug. Some platinum plugs have only the center electrode tipped with platinum, while others have both the center and ground electrodes platinum tipped. (It is not suggested that platinum plugs be used on vehicles with nitrous injection, however, there have been no problems reported using iridium plugs with nitrous).

Silver

The Silver spark plug (generally used by Bosch) are specifically designed for performance applications such as motorcycles, speedboats and sports cars. Bosch Silver plugs were designed to deliver critical requirements and handle the extreme pressures that exist today in high performance motor sports. The fine wire silver enhanced center electrode reduces misfires and ignite the air/fuel more easily to give peak power output.

Resistor

As well as reducing electrical noise for radio, television and mobile telephones etc, many modern ignition systems require resistor plugs to stop electrical noise from interfering with the vehicle's on-board electronic control units (ECUs). If non-resistor plugs are used in place of resistor ones, the result can be malfunction and in some cases immobilisation of the vehicle. Resistor spark plugs should always be fitted, therefore, where specified. The function of the resistor is to reduce electrical noise generated by the ignition system. The most effective place to situate a resistor in the high tension circuit is as close to the spark plug as possible. This makes the spark plug an ideal place to house the resistor. Because the resistance value is only approximately 5000 ohms, there is no detrimental effect on engine performance, power output, vehicle emissions etc.

Gasket Seat

Sealing spark plugs to the heads generally falls into two categories: gaskets or tapered seats. Gaskets have a washers to create the seal where as a tapered spark plug uses the taper of the plug to create the seal.

Tapered Seat

Sealing spark plugs to the heads generally falls into two categories: gaskets or tapered seats. Gaskets have a washers to create the seal where as a tapered spark plug uses the taper of the plug to create the seal.

Hesselman

A Hesselman engine is basically a spark-ignition engine, converted to run on heavier petroleum products such as oil, kerosene or diesel oil. The fuel is injected into the combustion chamber using an injection pump. Because of the engine low compression the fuel must be ignited by a spark plug, unlike the diesel engine, where the fuel ignites spontaneously by the heat generated by the high compression ratio. Hesselman engines were often started on gasoline and then switched to diesel or kerosene when at working temperature. Clearing the heavy oil for the next start was achieved by switching back to gasoline before stopping. It is the first spark ignition engine with direct injection of fuel into the cylinder.

Surface Gap

This type is used with certain high energy capacitor discharge ignition systems as recommended to overcome the worst fouling problems without over heating. The spark is fired across the insulator surface between the centre electrode and the shell. There is no heat range for surface gap plugs.