Available in 5k resistor and non resistor, these genuine LUCAS spark plug caps are an excellent and easy way to bulletproof your ignition wires.
If you are using an electronic ignition like Boyer Bransden, Tri-Spark, Pazon, or Vape- they all recommend using a resistor type spark plug cap with 5k ohm resistance. This helps suppress the electronic field from interfering with the ignition electronics. These caps are perfect for that, and are easy to install on your existing wires.
If you are running a Lucas or BTH magneto (or points ignition) and want the best spark possible, the non resistor caps are excellent for making a positive and waterproof connection to your plug. A definite upgrade from rubber caps which become looser over time.
Both of these are designed to push on to the spark plug terminal thread, which most can be removed by unscrewing. These caps can not be used with any plugs with a solid terminal. Most Champion and NGK plugs have removable terminal nuts. 
The inside of these caps are threaded for easy installation. Just cut your spark plug wire, put rubber boot on, and screw on for a perfect electrical connection. The plug end also has a rubber boot making these caps waterproof!
Since NGK has discontinued the manufacture of the popular LZFH and LB05E, LUCAS came to the rescue with these high quality replacements. Caps are phenolic resin and the boots are EPDM rubber for long life. The resistor caps have a 5k ohm ceramic resistor.
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