I like the OS A3 plug, i use it in all my engines including a TT GP.07, TT PRO.36, 2-TT PRO .46's, OS .40LA, Magnum .15XL and a .15XLS, Magnum .52XLS, the only two different plugs i use is an OS 8 in my OS .25FX( that's what it came with ) and i believe i have an Enya glow plug in a old Enya .45 that was given to me.