A block fitting for an air conditioning system comprising: a male block portion including a first aperture receiving a tube end therein, the male block portion including an annular shoulder surrounding the first aperture of the male block portion, the annular shoulder including an axially extending lip formed at a first end thereof, the lip having inner and outer circumferential surfaces; a female block portion including a first aperture receiving a tube end therein, the female block portion including an annular collar surrounding the first aperture of the female block portion and cooperating with the annular shoulder formed by the male block portion, the first aperture of the male block portion and the first aperture of the female block portion being substantially concentrically aligned, the female block portion having an annular groove between the aperture and the annular collar, the annular groove having inner and outer circumferential surfaces (102, 106) and the annular groove cooperating with the axially extending lip of the male block portion; a seal structure disposed radially inward from the axially extending lip of the male block portion and between the male block portion and the female block portion, the seal structure including a first seal portion produced from a plastically deformable metal or plastic material and having a free edge, the first seal portion surrounding the first aperture of the male block portion and the first aperture of the female block portion, and a second seal portion produced from an elastomer disposed on the free edge of the first seal portion; and a fastener engaging the male block portion and the female block portion, the fastener causing the male block portion and the female block portion to deform the first seal portion and provide a primary seal between the male block portion and the female block portion, and the fastener causing the male block portion and the female block portion to cooperate with the second seal portion and provide a secondary seal between the male block portion and the female block portion, wherein the primary seal and the secondary seal militate against a leakage of a fluid from the block fitting, wherein one of either the pair of tube ends or the male and female block portions have opposing sealing beads (48, 49) that plastically deform the first seal portion and provide the primary seal between the male block portion and the female block portion, the sealing beads (48, 49) facilitating the formation of the primary seal regardless of the presence of contamination at the seal structure, characterised in that a fine pilot is formed by a first gap between the inner circumferential surface of the axially extending lip and the inner circumferential surface of the annular groove and a coarse pilot is formed by a second gap between the outer circumferential surface of the axially extending lip and the outer circumferential surface of the annular groove, and an average width of the first gap forming the fine pilot is less than an average width of the second gap forming the coarse pilot, the inner and outer circumferential surfaces of the lip being tapered such that the axially extending lip is dual tapered to militate against a binding of the male block portion and the female block portion during assembly of the block fitting. a male block portion including a first aperture receiving a tube end therein, the male block portion including an annular shoulder surrounding the first aperture of the male block portion, the annular shoulder including an axially extending lip formed at a first end thereof, the lip having inner and outer circumferential surfaces; a female block portion including a first aperture receiving a tube end therein, the female block portion including an annular collar surrounding the first aperture of the female block portion and cooperating with the annular shoulder formed by the male block portion, the first aperture of the male block portion and the first aperture of the female block portion being substantially concentrically aligned, the female block portion having an annular groove between the aperture and the annular collar, the annular groove having inner and outer circumferential surfaces (102, 106) and the annular groove cooperating with the axially extending lip of the male block portion; a seal structure disposed radially inward from the axially extending lip of the male block portion and between the male block portion and the female block portion, the seal structure including a first seal portion produced from a plastically deformable metal or plastic material and having a free edge, the first seal portion surrounding the first aperture of the male block portion and the first aperture of the female block portion, and a second seal portion produced from an elastomer disposed on the free edge of the first seal portion; and a fastener engaging the male block portion and the female block portion, the fastener causing the male block portion and the female block portion to deform the first seal portion and provide a primary seal between the male block portion and the female block portion, and the fastener causing the male block portion and the female block portion to cooperate with the second seal portion and provide a secondary seal between the male block portion and the female block portion, wherein the primary seal and the secondary seal militate against a leakage of a fluid from the block fitting,