ID: 
2278
Maker's Name: 
Unknown
Dimensions: 
1.5 × 1.4 × 0.8 cm

The piece of Ferrite has two parallel holes. Insulated wire is looped through these holes around the central pillar. This was used in Black and White TV receiver tuners, to convert a balanced 300 Ohm twin line to an unbalanced 75 Ohm Coaxial cable. Hence the name Balun (BALanced UNbalanced).