A new shaft-mounted time domain reflectometry (TDR) probe design is described and evaluated. In contrast to previous shaft-mounted TDR probes (SMPs), the new design may be used to measure both dielectric constant (Ka) and bulk electrical conductivity (σa). Two SMP prototypes, 0.03 and 0.04 m long and having diameters of 0.006 m, were evaluated. The probes were calibrated in several fluids having different Ka and σa. A primary advantage of the SMP is minimal physical probe length without sacrificing accuracy of Ka readings. Accuracy of Ka measurements for the new probes was similar to that of standard 0.20-m-long three-rod probes.