These Rimfire spark plug prototypes were built by Paul Knapp in 1993. The first prototype (left front) is the surface-gap plug responsible for the “Rimfire” name and logo. The logo was designed by the late Chuck Driscol of Mesa AZ. All of the prototypes and early test samples were fabricated from Macor machinable ceramic.

About Rimfire Spark Plugs:

Paul Knapp designed a new 1/4-32 miniature spark plug in 1993 for the model airplane industry. The “Rimfire” name was derived from his first design; a surface-gap racing plug that performed exceptionally well at high speed but was too small to retain enough heat at low speed to prevent fouling. After several electrode designs, public demand led to the typical single ground electrode so the builder could change the gap for different applications.

In 1994, handmade samples were sent to many model racing enthusiasts in exchange for their reports on performance and/or failures. This valuable information was used to improve performance and reliability as Paul developed his new spark plug. By 1995, Rimfire spark plugs were used worldwide, and many were undergoing rigorous testing by several Aerospace companies such as XCOR Aerospace, Austrian Aerospace, German Aerospace, and NASA. The popularity among the model engine builders, the model airplane industry, and the need for different applications led to a variety of sizes and styles.

Bill Carpenter of CH Electronics in Wyoming produced the most reliable miniature CDI (capacitor discharge ignition) system used by modelers worldwide. In 1993 Mr. Knapp bet Mr. Carpenter that he could produce the world’s best, and most reliable, miniature spark plug to accompany the CH ignition system. Today’s line of “Rimfire” miniature spark plugs is the result of that bet.

Exhibit added: August 1, 2011 - Last modified: January 6, 2023

Presented by The Joe Martin Foundation for Exceptional Craftsmanship