A shaft assembly for a microwave ablation applicator which includes a shaft assembly and an antenna assembly located within the shaft assembly is disclosed. The shaft assembly comprises an elongate shaft (22) which extends from a first end (201) to a second end (202) thereof, and which defines therein a hollow inner volume and a longitudinal axis of the antenna assembly, and an applicator tip (24) mounted on the second end (202) of the elongate shaft (22). The applicator tip (24) defines an annular slot (70) with which the second end of the elongate shaft (22) engages. At least part a portion of the second end of the shaft (22) is of a fibre reinforced plastics material having a plurality of elongate fibres (52,56) bound in a plastics material (54), at least some of the fibres (56) extending at least partially circumferentially around the annular slot (70) of the applicator tip (24).
