Abstract: A hidden shackle style lock is disclosed. The lock includes a substantially cylindrical housing having a top surface, a bottom surface, and a curved side surface. The lock also includes a first cavity on the bottom surface of the housing extending part way along a thickness of the housing, and a second cavity on the side surface intersecting with the first cavity. A hollow sleeve is slidably attached within the second cavity. The sleeve includes a first end face, a second end face, and a third cavity. The third cavity extends from the first end face to the second face and is substantially coaxial with the second cavity. A shackle having a first end and a second end is fixedly coupled to the first end face of the sleeve. The lock also includes an interchangeable core having a first locking mechanism and a second locking mechanism lockingly disposed within the third cavity, and coupled to the straight shackle.