A connector assembly for an implantable medical electrical lead, the assembly having a central longitudinal axis and a uniform outer diameter conforming to a requirement for the connector to mate with a connector receptacle of an implantable medical device, and the assembly comprising: a plurality of contact rings (211,212,213) extending around the central longitudinal axis and being spaced apart from one another along a length of the assembly, each of the contact rings having an inner surface, and an outer contact surface, each outer contact surface defining the uniform outer diameter; a bulk of insulation supporting the plurality of contact rings and isolating the contact rings from one another, the bulk of insulation including a plurality of sealing surfaces (ss1-ss4), each sealing surface also defining the uniform outer diameter of the assembly, and characterised by the bulk of insulation including a shank, the shank defining a distal end of the bulk of insulation, and the shank having an asymmetric profile, a first sealing surface of the plurality of sealing surfaces extending from a proximal end of the bulk of insulation to a first ring of the plurality of contact rings, a second sealing surface of the plurality of sealing surfaces extending between the first contact ring and a second contact ring of the plurality of contact rings, and a third sealing surface of the plurality of sealing surfaces extending distally from the second contact ring; at least one conductor pin (11,12,13,14) extending within the bulk of insulation, a distal end of each conductor pin protruding distally from the bulk of insulation and being exposed alongside the shank thereof, and a proximal end of a first conductor pin of the at least one conductor pin being coupled to the inner surface of the first contact ring; and a core extending within the bulk of insulation, the core being aligned along the central longitudinal axis of the assembly. a plurality of contact rings (211,212,213) extending around the central longitudinal axis and being spaced apart from one another along a length of the assembly, each of the contact rings having an inner surface, and an outer contact surface, each outer contact surface defining the uniform outer diameter; a bulk of insulation supporting the plurality of contact rings and isolating the contact rings from one another, the bulk of insulation including a plurality of sealing surfaces (ss1-ss4), each sealing surface also defining the uniform outer diameter of the assembly, and characterised by the bulk of insulation including a shank, the shank defining a distal end of the bulk of insulation, and the shank having an asymmetric profile, a first sealing surface of the plurality of sealing surfaces extending from a proximal end of the bulk of insulation to a first ring of the plurality of contact rings, a second sealing surface of the plurality of sealing surfaces extending between the first contact ring and a second contact ring of the plurality of contact rings, and a third sealing surface of the plurality of sealing surfaces extending distally from the second contact ring; at least one conductor pin (11,12,13,14) extending within the bulk of insulation, a distal end of each conductor pin protruding distally from the bulk of insulation and being exposed alongside the shank thereof, and a proximal end of a first conductor pin of the at least one conductor pin being coupled to the inner surface of the first contact ring; and a core extending within the bulk of insulation, the core being aligned along the central longitudinal axis of the assembly.