Balance with inertia adjustment for timepieces, including a hub defining the pivot axis of the balance, a rim, a web extending between a lower plane and an upper plane on either side of a median plane, the web including at least one arm connecting the rim to the hub, the arm including a housing configured to receive and hold in place at least one inertia block. According to the invention, the inertia block has a front face and a rear face and is integrated in the balance arm, so that the front face and rear face are substantially in the upper plane and the lower plane.

A timepiece assembly including a first component and a second component assembled under stress, wherein at least one part of the surface of the assembly is coated with a protective layer intended to cover defects such as cracks or incipient cracks after assembly. It also relates to the method for manufacturing this assembly.

A horological assembly for a horological regulating member, including a balance spring (25) having a coiled flexible strip (2); a device for adjusting its rigidity which includes a flexible element (5) arranged in series with the strip and connecting one end (4) of said strip to a rigid support (17), the flexible element having a rigidity greater than that of the strip. The adjustment device includes a pre-stressing device (6) for applying a variable force or torque to the flexible element to vary the rigidity of the flexible element. A stud-holder (1) is configured to suspend the balance spring and includes a main body (30) connected to the flexible element, and a secondary body (33) connected to the pre-stressing device, the secondary body (33) being movable relative to the main body (30) and being connected to the main body by a flexure bearing (20).