Self-drilling dowel assembly with an annular drill bit

Self-drilling dowel assembly comprising an axially elongated expansion sleeve forming an axially extending bore therethrough and having a first end and a second end, a drill bit formed on the first end of said expansion sleeve, a partition wall located within the bore in said expansion sleeve and extending transversely across and dividing the bore into a first blind bore extending from the first end of said sleeve to said partition wall and a second blind bore extending from the second end of said sleeve to said partition wall, a spreader positioned within the second blind bore in said sleeve and said spreader being axially displaceable within the bore in the direction from the second end toward the first end in frictional contact with the surface of the second bore for expanding said sleeve outwardly, wherein the improvement comprises that the first blind bore in said expansion sleeve has a diameter in the range of 0.5 to 0.9 times the exterior diameter of said expansion sleeve at the first end thereof.