A downhole tool comprises a bottom hole assembly having a central opening therethrough and an insert having an inner diameter within the bottom hole assembly. The insert 70 is made of a hardened material to protect the bottom hole assembly from erosion as a fluid passes through the central opening and the insert. The insert 70 can be trumpet shaped and brazed or epoxied in place. The insert can be formed from discs or washers (figures 2 and 3) which define a passage of a throat. The hardened material can be polycrystalline diamond. The bottom hole assembly can be a nozzle, throat or diffuser.
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