A balun (from "balanced to unbalanced", originally, is an electrical device that allows balanced and unbalanced lines to be interfaced without disturbing the impedance arrangement of either line.
 
This is a handy device for portable or tempoary antenna installations - you'll need two lengths of wire that attach on the nut & bolt side and the Balun will allow a match to a 50 Ohms cable / Transceiver.
 
Balun operating power up to 100W SSB Suitable HF Shortwave Antennas between frequency of 3-30mhz ideal for outdoor activations / Portable QRP Stations (Beware of using high power/continuous transmissions with data modes such as FT8 due to heating of the core resulting in high SWR)
 
Good for matching antenna to receiver only equipment as well - may inporove received signal as it will allow maximum power transfer (maximum received signal) to be transferred from the antenna to the receiving equipment.  ALso can help reduce noise pick-up on feed lines.
 
THis little Balun is light -  only 46g and case is accessible for modification or repair.  Also allows for waterproofing if required.
 
Product size: 91x36x26MM/3.58x1.42x1.02inch including terminal
housing size: 61x36x26MM/2.4x1.42x1.02inch