Switch for ultrasonic surgical tool

A switch unit so mountable to a distal end of a handpiece of an activatable surgical tool as to be contactable by a finger of a hand manipulating the handpiece, said switch unit being radially symmetrical and having an intermediate waist portion, wherein the waist portion comprises an inner deformable member having in transverse cross-section an outer profile comprising a plurality of flat surfaces and at least one apex and an inner profile defining a channel therethrough and having one or more first switch contacts mounted or affixed thereto such that a first switch contact is mounted or affixed opposite each flat surface;

• and an outer deformable member extending circumferentially around the waist portion, which, in an undeformed state, contacts the inner deformable member only at the or each apex, wherein, in use, pressure applied by a finger deforms the outer deformable member to exert a force on the inner deformable member at a location remote from the or each apex such that each first switch contact moves in an inward direction towards a corresponding second switch contact located within the channel, thereby activating the tool.