These cable joiners are made by CARROLL who are known throughout the Auto Electrical industry for supplying high quality wiring accessories......

you are purchasing a packet of 10 joiners made to suit 8B&S (10mm² cable). 

Centre of joiner there is a tag to allow you to push cable against it from each side then crimp....

These can be used to join cbale on dual battery systems, DC-DC charger setups, and much more.

Also used in industrial 240+ volt applications