A rock bolt (1) comprises a tubular body (4) defining a tubular bore (5) for receiving an adhesive or cement filled cartridge (18). A plug (8) is mounted in the bore (5). The plug (8) is displaceable along the bore (5) and sealingly engages the tubular body (4). A bolt head (7) is located at or adjacent a second end (3) of the rock bolt (1). A detent arrangement (10, 12) restrains the plug (8) in a position adjacent an opening at the first end (2) of the rock bolt (1).