RIDGID 39873 ST-33Q Interface Circle Board Kit. The RIDGID ST Line Transmitter Series are top-of-the-line transmitters designed for inducing current onto a target line for tracing. These Transmitters are lightweight and compact, they can transmit simultaneously and feature audio feedback for confirmation of a good circuit. the RIDGID 39873 ST-33Q Interface Circle Board Kit is a genuine part designed specifically for the ST-33Q Transmitter, and is manufactured by RIDGID. This RIDGID 39873 ST-33Q Interface Circle Board Kit is fully covered under RIDGID's 3-year limited performance warranty and lifetime warranty to be free of material defects.