A gyratory crusher frame part comprising: a topshell mountable upon a bottom shell, the topshell having an annular wall extending around a longitudinal axis of the frame part; a spider having a plurality of arms extending radially outward from a cap positioned at the longitudinal axis, each arm of the plurality of arms having an first portion extending generally in a radially outward direction from the cap and a second portion extending generally in an axial direction from an outer region of the first portion; an upper annular flange positioned between the second portion of each arm and the annular wall, the upper flange having an outer circumferential perimeter and an inner circumferential perimeter relative to the longitudinal axis; a lower flange axially separated from the upper flange by a section of the wall; the topshell comprising an outward facing surface and an inward facing surface relative to the longitudinal axis, the annular wall being defined between the outward and inward facing surfaces; wherein the section of the wall of the topshell neighbouring the upper flange comprises a concave section at the outward facing surface and substantially an upper half of the concave section in the axial direction closest to the upper flange is a substantially uniform curve extending continuously in the circumferential direction around the longitudinal axis; and wherein a majority of a lower half of the concave section in the axial direction closest to the lower flange comprises a curvature profile in the axial direction substantially equal to a curvature profile in the axial direction of the upper half; characterised in that: the outward facing surface of the concave section comprises a curvature defining a substantially uniform curve extending continuously in the axial direction between the upper flange and the lower flange. a topshell mountable upon a bottom shell, the topshell having an annular wall extending around a longitudinal axis of the frame part; a spider having a plurality of arms extending radially outward from a cap positioned at the longitudinal axis, each arm of the plurality of arms having an first portion extending generally in a radially outward direction from the cap and a second portion extending generally in an axial direction from an outer region of the first portion; an upper annular flange positioned between the second portion of each arm and the annular wall, the upper flange having an outer circumferential perimeter and an inner circumferential perimeter relative to the longitudinal axis; a lower flange axially separated from the upper flange by a section of the wall; the topshell comprising an outward facing surface and an inward facing surface relative to the longitudinal axis, the annular wall being defined between the outward and inward facing surfaces; wherein the section of the wall of the topshell neighbouring the upper flange comprises a concave section at the outward facing surface and substantially an upper half of the concave section in the axial direction closest to the upper flange is a substantially uniform curve extending continuously in the circumferential direction around the longitudinal axis; and wherein a majority of a lower half of the concave section in the axial direction closest to the lower flange comprises a curvature profile in the axial direction substantially equal to a curvature profile in the axial direction of the upper half; characterised in that: the outward facing surface of the concave section comprises a curvature defining a substantially uniform curve extending continuously in the axial direction between the upper flange and the lower flange.