Patent ID: 7307204

Claim:
A drum comprising: a cylindrical body having an opening, an outer circumference, and axial direction; a head, which covers the opening of the body, the head including a rim and an outer circumference; a cylindrical head frame, which is fitted to the outer circumference of the body, the head frame retaining the rim of the head and being movable along the axial direction of the body; a hoop provided at the outer circumference of the head, the hoop abutting against the head frame to press the head frame along the axial direction of the body so that tension is applied to the head, the hoop including a plurality of mounting holes; a plurality of fasteners located at the outer circumference of the body, each fastener being located opposite to the hoop with the head frame located in between, and each fastener including a nut; a plurality of coupling bolts, which extend along the axial direction of the body, each coupling bolt including a head, with the head located opposite to the nut of one of the fasteners with the hoop located in between, and each coupling bolt being inserted in one of the mounting holes and threaded to said nut so that the hoop is coupled to the fastener; and a plurality of loosening prevention structures, each loosening prevention structure being located between the head of one of the coupling bolts and the hoop, and including an annular elastic body through which said one of the coupling bolts is inserted and a deformation restricting member, which is discrete from the head of the one of the coupling bolts and is placed between a bottom surface of the head and the annular elastic body to restrict deformation of the elastic body along said axial direction, wherein each deformation restricting member includes an annular portion through which the one of the coupling bolts is inserted and a cylindrical portion extending from the annular portion towards the hoop, wherein the cylindrical portion has an inner surface positioned adjacently to an outer circumference of the elastic body, and wherein the cylindrical portion is shorter in said axial direction than the elastic body along said axial direction, such that when the elastic body is not compressed along said axial direction, a space is formed between an end of the cylindrical portion and the hoop, and as the coupling bolt is tightened relative to the nut, the elastic body is compressed a length corresponding to and up to a length of the space in said axial direction and the cylindrical portion abuts against the hoop and the head of the bolt.