Engine overhaul shops do not necessarily have a full in-house capability to overhaul all the engine components. Specialised re-work is often carried out by third party component overhaulers.
Items that are often sent to third party overhaulers include compressor blades and vanes, discs and shafts, combustion liners, bearings, turbine blades, and turbine vanes.
One third party overhauler specialising in turbine vanes may overhaul vanes for ten or more overhaul shops.
This allows the third party overhauler to invest in expensive equipment needed for a particular process and reduces the price of the overhaul of the vanes. Also, the third party overhauler is subject to regular quality audits from all its customers and often becomes a world-wide centre of excellence for that work.