A stemming plug (10,40,50,60) for stemming a blast hole in a mine, the plug (10,40,50,60) comprising: first (12,42,52,62) and second (14,44,54,62') elongate wedge-shaped members manufactured from a suitable plastics material; the first wedge-shaped member (12,42,52,62) having a larger end with a face (16,64) sloping towards a smaller end, the sloping face (16,64) being received in sliding relationship with a matching face (18,64') of the second wedge-shaped member (14,44,54,62') wherein, in use, when the first wedge-shaped member (12,42,52,62) is positioned with its larger end nearest to an explosive material in the blast hole it has a larger surface area facing the explosive material than the second wedge-shaped member (14, 44,54,62'); and, wherein the second wedge-shaped member (14,44,54,62') is provided with a retraction loop (38,46,56,76) for retracting the plug (10,40,50,60) from the blast hole after installation in a case of misfire; whereby, in use, when a shockwave from initiation of the explosive material in the blast hole encounters the first wedge-shaped member (12,42,52,62) it acts as a piston, sliding on the second wedge-shaped member (14,44,54, 62') so that both wedge-shaped members exert diametrically opposed forces against the wall of the blast hole to lock the plug (10,40,50,60) in place, the stemming plug being characterised in that the retraction loop (38,46,56,76) interferes enough with the blast hole to retain the placement of the second wedge-shaped member (14,44,54,62') in the hole, and provides the frictional resistance to movement required, as well as a marginal increase in mass for the second wedge-shaped member (14,44,54,62'). first (12,42,52,62) and second (14,44,54,62') elongate wedge-shaped members manufactured from a suitable plastics material; the first wedge-shaped member (12,42,52,62) having a larger end with a face (16,64) sloping towards a smaller end, the sloping face (16,64) being received in sliding relationship with a matching face (18,64') of the second wedge-shaped member (14,44,54,62') wherein, in use, when the first wedge-shaped member (12,42,52,62) is positioned with its larger end nearest to an explosive material in the blast hole it has a larger surface area facing the explosive material than the second wedge-shaped member (14, 44,54,62'); and, wherein the second wedge-shaped member (14,44,54,62') is provided with a retraction loop (38,46,56,76) for retracting the plug (10,40,50,60) from the blast hole after installation in a case of misfire; whereby, in use, when a shockwave from initiation of the explosive material in the blast hole encounters the first wedge-shaped member (12,42,52,62) it acts as a piston, sliding on the second wedge-shaped member (14,44,54, 62') so that both wedge-shaped members exert diametrically opposed forces against the wall of the blast hole to lock the plug (10,40,50,60) in place, the stemming plug being characterised in that the retraction loop (38,46,56,76) interferes enough with the blast hole to retain the placement of the second wedge-shaped member (14,44,54,62') in the hole, and provides the frictional resistance to movement required, as well as a marginal increase in mass for the second wedge-shaped member (14,44,54,62').