All our engines use plugs with M14 x 1.25 threads. T4 engines and T1 with certain Mexican (and some exotic performance) heads call for nominally 3/4" or 19mm long threads. Standard T1 engines with OG spec heads call for nominally 1/2" 0r 13mm long threads. So, if you're measuring and counting, long: 19 / 1.25 = 15 threads, short: 13 / 1.25 = 10 threads.
