These are simple pigtail common mode chokes consisting of RG58 cable with a PL259 on one end and SO239 on the other.  Approx 5-6cm of space between the core and the connectors.
 
The standard widing is 12 times around a 240-43 Toroid core.  Maximum power is 400w.
 
If placed between you tranceiver and antenna you will get sufficient choking effect to isolate your Tranceiver from currents or noise passing on the outside of your coax.
 
If you have purchased one of our EFHW or EFRW antennas you should position the toroid at the receiver and and then have the remaining coax going to the antenna transformer.
 
NOTE
These are built to order and may take a day or so longer than quoted for dispatch.