Components and replacement parts for ultrahigh-pressure fluid jet systems, namely, check valve bodies; ultrahigh-pressure cylinders; machine parts, namely, plungers for ultrahigh-pressure intensifier pumps, plungers for ultrahigh-pressure direct drive pumps, and end caps for ultrahigh-pressure pumps; orifice assemblies; machine parts, namely, orifice mounts and orifices; mixing tubes; nozzles; cutting heads and structural parts thereof; abrasive metering systems comprised of storage tanks, pipelines, and gauges, and structural parts thereof; filters for ultrahigh-pressure fluid jet systems; hydraulic cartridge assemblies containing hydraulic cartridge piston, seals and o-rings; seal assemblies and structural parts thereof; o-rings; valves for pumps; pressure springs; wear inserts; linear actuator assemblies; bearings; collets; repair kits for valves primarily comprised of poppets, seals, valve seats and o-rings; and low pressure cylinder repair kits primarily comprised of seals and o-rings