Well, I just went out and put the mic' on both the L-o-Matic and the duraspark II shafts' both measure .514 to .515 or thera-abouts, just over a 1/2" in OD. So, Addo--which one do I need? I am sure this is the one Mike carries or is he going with both? And, I measured just below the gear at about an 1/8".