When Connectorised Fibre first came out there was no Digital Voice and Openreach were in the process of Phasing out FVA.
As people would retain their Copper Voice Line they came out with a Fibre/Copper Hybrid Cable. The Larger one housed the Fibre and the smaller one a Single Copper Pair.
Its hardly used anymore now most people have Digital Voice as Engineers can not just use the Single Fibre ROC or RFOD Cable.
