A disk brake disk or disk, said disk being made in a single piece by co-casting two materials, comprising: - a bell made of a first material and adapted to connect said disk to a rotating support; - a braking band made of a second material; - said disk defining an axial direction (A-A) coinciding with, or parallel to, a rotation axis (X-X), a radial direction (R-R) orthogonal to said rotation axis (X-X) and defining a radially outer direction when moving away from said rotation axis (X-X), as well as a radially inner direction when moving close to said rotation axis (X-X), a circumferential direction (C-C) orthogonal to said axial direction (A-A) and to said radial direction (R-R), as well as a tangential direction (T-T) orthogonal to said axial direction (A-A) and to said radial direction (R-R) in a point of intersection of said axial direction (A-A) and to said radial direction (R-R); wherein - said bell comprises a bell body having a radially outer bell body portion; - said bell forms a plurality of bell projections or projections in a single piece, which radially protrude from said radially outer bell body portion according to said radially outer direction; - each projection comprises a projection base or base, arranged close to said radially outer bell body portion, and a distal projection portion or distal portion, arranged far from said radially outer bell body portion; wherein - said braking band has a braking band body; - said braking band body is connected and intimately coupled to said distal portion wrapping said distal portion all around and at the top; characterized in that - adjacent bases of said plurality of projections are joined to one another by a bell rib or rib made in a single piece with said bell body; - each rib comprises an inner axial rib face or inner face and an opposite outer axial rib face or outer face; - said braking band body is connected and intimately coupled to said inner face, leaving said outer face free and thus externally facing said disk. - a bell made of a first material and adapted to connect said disk to a rotating support; - a braking band made of a second material; - said disk defining an axial direction (A-A) coinciding with, or parallel to, a rotation axis (X-X), a radial direction (R-R) orthogonal to said rotation axis (X-X) and defining a radially outer direction when moving away from said rotation axis (X-X), as well as a radially inner direction when moving close to said rotation axis (X-X), a circumferential direction (C-C) orthogonal to said axial direction (A-A) and to said radial direction (R-R), as well as a tangential direction (T-T) orthogonal to said axial direction (A-A) and to said radial direction (R-R) in a point of intersection of said axial direction (A-A) and to said radial direction (R-R); wherein - said bell comprises a bell body having a radially outer bell body portion; - said bell forms a plurality of bell projections or projections in a single piece, which radially protrude from said radially outer bell body portion according to said radially outer direction; - each projection comprises a projection base or base, arranged close to said radially outer bell body portion, and a distal projection portion or distal portion, arranged far from said radially outer bell body portion; wherein - said braking band has a braking band body; - said braking band body is connected and intimately coupled to said distal portion wrapping said distal portion all around and at the top; characterized in that - adjacent bases of said plurality of projections are joined to one another by a bell rib or rib made in a single piece with said bell body; - each rib comprises an inner axial rib face or inner face and an opposite outer axial rib face or outer face; - said braking band body is connected and intimately coupled to said inner face, leaving said outer face free and thus externally facing said disk.