A sealing plug for blind installation in a suitable hole thereby to plug and seal the hole, which sealing plug has a sleeve (1); a stem (2) having a head at least part of which is radially enlarged with respect to the remainder of the stem (2); the stem head (4) having a shoulder, the shoulder being provided with an annular protrusion (9); the stem (2) protruding from one end of the sleeve (1), and the annular protrusion (9) abutting the other end of the sleeve (1); the stem head (4) being of a material which is harder than that of the sleeve (1) and being formed with a weakened portion (3) intermediate the head (4) and the part of the stem remote therefrom; whereby, when the sealing plug is inserted in a suitable hole, with the sleeve (1) entirely within the hole, and increasing force is applied to the stem (2) with respect to the sleeve (1), axial compression is applied by the shoulder to the sleeve material abutting it, thereby causing the annular protrusion (9) on the stem head (4) to embed into the sleeve (1), and the sleeve to deform and expand radially to engage with the wall of the hole, and thereafter the stem (2) breaks at the weakened portion so that the head (4) remains in the sleeve (1).