Aviation Spark Plug Gaskets are manufactured to precise dimensions and material standards, based on the effective reach of a spark plug as determined by its installed thickness. An ideal installation has the firing end of the plug flush with the combustion chamber wall with no exposed threads on the plug or the cylinder bushing. Exposed threads can become hot spots initiating preignition. Use and installation of proper gaskets are essential to reliable engine operation. Double gasketting a spark plug or use of non-standard thin gaskets will expose threads, contributing to engine-damaging preignition. Use new copper gaskets to ensure a tight, gas-sealed spark plug.