Open clamp meter. Hydraulic power tongs are an open-type power tong used to load and unload oil pipe threads in oilfield workover operations. They require the use of a pocket meter that detects voltage, current and continuity, that is, an open-ended clamp meter. Hydraulic power tongs are a type of workover tool that utilizes the power of a workover rig to mechanically attach and remove threading tools. It has obvious advantages and is easy to use.