RJ12 plugs fit all RJ11 sockets. Uses a special and expensive extended Shielded RJ12 plugs these are much stronger/better crimp so stop any chance of cable pull out due to the cable being strained at angles!
eBay
BIGTREETECH RJ11 to Can Cables for Octopus V1.1 Octopus Pro F446 F429 150MM XH2.54-2P 3D Printer Accessories
Aliexpress UK
This cable can be used to connect your ADSL Modem (with an RJ11socket) to the Filter/Splitter. plugged into your BT ADSL enabled wall socket. Connection: 4 Pin RJ11 to RJ11. Suite for ADSL connection.
eBay
Have an RJ11 compatible ADSL modem?. AVOID PHONE CORDS WITH shoddy wiring that leaves your CONNECTION POOR and you frustrated.
eBay
This product is a brand new RJ11 to RJ11 DSL/Phone cable, suitable for connecting your your router to your phone socket (please see my other listings if you need a microfilter). The cable is compatible with all universal brands and is made in China. The connector A is an RJ-11, and the connector B is a DSL/Phone (RJ-11) male, making it easy to create a reliable connection for your internet service.
eBay
eBay
This high quality cable can be used to connect your ADSL Modem (with an RJ11 socket) to the Filter/Splitter plug in your BT ADSL enabled wall socket. The RJ11 Pins are gold plated and 100% Copper to support a fast connection speed. These are able to connect 56k Fax/Data/Voice. RJ11 High Speed Broadband ADSL Internet Phone Modem Internet BT Cable Plug 8M
eBay
RJ11 Male to RJ11 Female. RJ11 Extension Lead. Good Quality Flat 28 AWG Cable.
eBay
Bought it for my broadband which I now swapped to Fibre and no longer need this wire. Still works perfectly and looks great. All yours if you’re interested 😁 10 meter RJ11 Cable ADSL BT SKY Broadband Modem Internet DSL Land Line Home Phone Lead
eBay