An end coupling 1, 19 for a shaft 2 of a rock bolt 50 comprises a body 6 having a lead portion 8 with a leading end 9, and a tail portion 10 with a trailing end 11. The tail portion 10 is arranged to be connected to a drive to impart rotation to the coupling about its axis. The body 6 defines a passage 7 extending between the leading and trailing ends and a first portion 12 of the passage 7 extends from the leading end 9 and has a first diameter. A second portion 15 of the passage 7 is disposed adjacent the first portion 12 and has a second diameter that is larger than said first diameter. A first thread 14 extends along at least part of the first portion 12 of the passage 7 and is arranged to engage an external thread 4 on the rock bolt shaft 2. A rock bolt assembly incorporating the end coupling 1, 19 is also disclosed.