A clamp mechanism for a power distribution line sensor including a drive rod having a first rod portion with a spiral thread formed in a first-handed thread direction, a second rod portion with a spiral thread formed in an opposite-handed thread direction, and a coupling end portion. The mechanism also includes a first clamp portion having a first drive block engaged with the first rod portion and a first clamp arm having a pin-in-slot connection to that drive block, as well as a second clamp portion having a second drive block engaged with the second rod portion and a second clamp arm having a pin-in-slot connection to that drive block. The first clamp arm and the second clamp arm are secured to each other, yet rotatable with respect to each other, at a proximal end of each respective clamp arm. A clamp block may function as part of the securement.