A housing part for a measurement device, said housing part having a microwave-permeable glass or ceramic window and comprising: a single body made of metal; the single body has an outer circumferential side wall with an upper end and a lower end and an inner disc-shaped base wall located between the upper and lower ends (23, 24), the side wall and the base wall defining two partially enclosed areas (25, 26); the base wall comprises a flat circular center portion surrounded by an annular zone of reduced wall thickness on both upper and lower surfaces (31, 32) of the base wall, the circular center portion projecting above and below the surrounding annular zone of reduced wall thickness; the center portion comprises a central hole into which the glass or ceramic window is fused, the window forming flush surfaces coextensive with the upper and lower surfaces (31, 32) of the circular center portion; the upper one of the two partially enclosed areas (25, 26) accommodates a first dielectric matching element and a first microwave guide; the first dielectric matching element has a tapered or stepped profile and a bottom flange portion that is pressed against and radially interferes with the upper surface of the circular center portion of the base wall; the first microwave guide has a first flange providing a first end face and an inner shoulder for accommodating and matching with the bottom flange portion of the first dielectric matching element; a first thrust collar is provided on the first microwave guide to press the first flange with the first end face against the upper surface of the base wall outside its circular center portion; the lower one of the two partially enclosed areas (25, 26) accommodates a second dielectric matching element and a second microwave guide; the second dielectric matching element has a tapered or stepped profile and a bottom flange portion that is pressed against and radially interferes with the lower surface of the circular center portion of the base wall; and the second microwave guide has a second flange providing a second end face and an inner shoulder for accommodating and matching with the bottom flange portion of the second dielectric matching element; a second thrust collar is provided on the second microwave guide to press the second flange with the second end face against the lower surface of the base wall outside its circular center portion. a single body made of metal; the single body has an outer circumferential side wall with an upper end and a lower end and an inner disc-shaped base wall located between the upper and lower ends (23, 24), the side wall and the base wall defining two partially enclosed areas (25, 26); the base wall comprises a flat circular center portion surrounded by an annular zone of reduced wall thickness on both upper and lower surfaces (31, 32) of the base wall, the circular center portion projecting above and below the surrounding annular zone of reduced wall thickness; the center portion comprises a central hole into which the glass or ceramic window is fused, the window forming flush surfaces coextensive with the upper and lower surfaces (31, 32) of the circular center portion; the upper one of the two partially enclosed areas (25, 26) accommodates a first dielectric matching element and a first microwave guide; the first dielectric matching element has a tapered or stepped profile and a bottom flange portion that is pressed against and radially interferes with the upper surface of the circular center portion of the base wall; the first microwave guide has a first flange providing a first end face and an inner shoulder for accommodating and matching with the bottom flange portion of the first dielectric matching element; a first thrust collar is provided on the first microwave guide to press the first flange with the first end face against the upper surface of the base wall outside its circular center portion; the lower one of the two partially enclosed areas (25, 26) accommodates a second dielectric matching element and a second microwave guide; the second dielectric matching element has a tapered or stepped profile and a bottom flange portion that is pressed against and radially interferes with the lower surface of the circular center portion of the base wall; and the second microwave guide has a second flange providing a second end face and an inner shoulder for accommodating and matching with the bottom flange portion of the second dielectric matching element; a second thrust collar is provided on the second microwave guide to press the second flange with the second end face against the lower surface of the base wall outside its circular center portion.