The MFJ-260C is an air cooled, non-inductive resistor in a perforated metal housing. It has SO-239 connectors. You can handle a full load for 30 seconds. Silk-screened derating curve to 5 minutes. Handles 300 Watts. SWR below 1.1:1 to 30 MHz, 1.5:1 from 30 to 650Mhz. It measures a super compact 2 1/4x2 1/4x7 inches.