To receive two cores, send an A5-size padded bag with your address and
49p return postage to:
Andy Lake
Broadridge Nook
Morchard Bishop
CREDITON
Devon EX17 6RH
These cores have several uses, including reduction of RF currents on
the outers of interconnecting and mains leads.
See also Ian White's (G3SEK) article
on an RF clip-on ammeter.