A turbine for a turbocharger, the turbine having: a turbine housing defining a gas inlet; and a turbine wheel positioned for rotation within the turbine housing about an axis; a ring-shaped shroud defining a plurality of slots (130; 230; 730), and encircling the axis; a nozzle ring supporting a plurality of vanes (107; 207; 307 407; 507; 707) which extend from the nozzle ring parallel to the axis, and project through respective ones of the slots, each of the vanes being spaced from the axis by a nozzle radius defined as the radius of a circle centred on the turbine axis and passing through the centroids of the profiles of the vanes (107;207;307;407;507;707); and a coupling mechanism for coupling the shroud to the nozzle ring; each of the slots having an inwardly-facing slot surface, and each of the vanes having an axially-extending vane surface which includes (i) a vane outer surface (142, 242; 742) facing an outer surface (147; 247; 747) of the corresponding slot, (ii) an opposed vane inner surface (141, 241) facing an inner surface (146; 246) of the corresponding slot, and (iii) a median line (151; 251; 751) between the vane inner surface and the vane outer surface extending from a first end of the vane to a second end of the vane; the turbine characterized in that: the vane surface includes a first portion (145; 245; 745), extending along at least 80% of the length of the median line, and facing a corresponding first portion (145; 245; 745) of the slot surface, wherein, at room temperature, the respective profiles of the first portion of the vane surface and the first portion of the slot surface diverge from each other by no more than 0.35% of the nozzle radius. a turbine housing defining a gas inlet; and a turbine wheel positioned for rotation within the turbine housing about an axis; a ring-shaped shroud defining a plurality of slots (130; 230; 730), and encircling the axis; a nozzle ring supporting a plurality of vanes (107; 207; 307 407; 507; 707) which extend from the nozzle ring parallel to the axis, and project through respective ones of the slots, each of the vanes being spaced from the axis by a nozzle radius defined as the radius of a circle centred on the turbine axis and passing through the centroids of the profiles of the vanes (107;207;307;407;507;707); and a coupling mechanism for coupling the shroud to the nozzle ring; each of the slots having an inwardly-facing slot surface, and each of the vanes having an axially-extending vane surface which includes (i) a vane outer surface (142, 242; 742) facing an outer surface (147; 247; 747) of the corresponding slot, (ii) an opposed vane inner surface (141, 241) facing an inner surface (146; 246) of the corresponding slot, and (iii) a median line (151; 251; 751) between the vane inner surface and the vane outer surface extending from a first end of the vane to a second end of the vane; the turbine characterized in that: the vane surface includes a first portion (145; 245; 745), extending along at least 80% of the length of the median line, and facing a corresponding first portion (145; 245; 745) of the slot surface, wherein, at room temperature, the respective profiles of the first portion of the vane surface and the first portion of the slot surface diverge from each other by no more than 0.35% of the nozzle radius.