The invention relates to a protection dish (32) for a counterbore formed in an aircraft mechanical part, said protection dish (32) having an axial cross-section about an axis (A) having substantially the shape of a U, and comprising a substantially annular wall (34) of axis (A) and a substantially cylindrical rim (36) of axis (A) connected to an outer periphery of said substantially annular wall (34). The invention is characterised in that said dish (32) is configured to be deformed in response to an axial stress (F) of a determined intensity applied on the substantially annular wall (34) thereof from a first state, wherein the substantially cylindrical rim (36) has a first transverse dimension (E) relative to axis (A), to a second state, wherein the substantially annular wall (34) being deformed, the cylindrical rim (36) has a second transverse dimension (E′) relative to the axis (A) that is greater than the first transverse dimension (E) along a transverse direction (T) determined relative to axis (A).