In reducing and in preventing the damage to bridge structures, knocking-off members or devices are adoptable. Then, it is important to understand their brittle fractures and to obtain their controlled and stable breaking loads. In this paper, high strength bolts inserted a slit around their shanks are dealt with among the knocking-off members and their breaking characteristics are investigated through tensile and shear break tests. It is concluded that the height and depth of the slit is not sensitive to the shear breaking load of the slitted bolts and the breaking load is approximately figured out by using the cross sectional area of the slitted part and tensile strength of the bolt material.