Abstract: A mixing head for high pressure mixing of reactive chemicals defines a mixing chamber for receiving and mixing oppositely directed impinging chemicals and having an outlet through which the chemicals are discharged after mixing. A separate tubular nozzle assembly for each chemical is replaceably mounted in the body of the mix head and has an inlet for receiving one of the chemicals and an orifice communicating with the mixing chamber. Each nozzle assembly includes a nozzle body and an annular sleeve or ring shaped orifice member of abrasion resistant material defining the orifice and a tubular support fabricated from a non-metallic material, e.g., an internally lubricated super polyamide, snugly spacing the annular orifice member from portions of the nozzle body defining the associated passage and also interfitting with the annular orifice member in supporting relation.