that is an accelerator to help reduce interference form the bellwire on terminal 3. you get better affect by removing the bellwire on terminal 3 as not required
the MK3 insert looks like that but it has a broadband socket in the top and acts as a filter so filters are no longer needed on any other sockets downside is if you use that then hub needs to be connection to the master socket unless you wire it differently
socket would look like this with MK3 inserted
Thanks for all that.
At the end of the day, it looks like it would then be easier to pay for th engineer to come to improve the service.
That is my question answered !
you could just get a local telecom engineer to tidy up your wiring and save some money
Thanks for that. I thuoght that only Bt Openreach engineers could touch or improve BT sockets/wiring etc.