A syringe and detachable needle assembly having reduced dead space features comprising: an elongate syringe barrel having a longitudinal axis, an inside surface defining a chamber for retaining fluid, an open proximal end, an open distal end including a collar and a distally facing annular surface projecting inwardly from said collar, a portion of said collar having a cylindrically shaped, axially aligned circular side wall; a needle assembly including a hub having a body portion including a proximal end, a distal end, a conduit therethrough, a proximally facing annular surface on said body portion contacting said annular surface of said barrel forming a primary seal between said hub and said barrel, said hub further including an outwardly projecting annular sealing ring sealingly engaging said circular side wall of said collar forming a secondary seal between said hub and said barrel, said needle assembly further including a cannula having a distal end, a proximal end and a lumen therethrough, said proximal end of said cannula being connected to said distal end of said hub so that said lumen is in fluid communication with said chamber; and means for releasably engaging said hub to said collar including at least one thread on an inside surface of said collar or at least one thread on an outside surface of said hub, characterized by wherein distally facing annular surface of the barrel is flat and proximally facing annular surface of the hub is flat; two thread engaging projections on opposite sides of the hub; wherein during installation, rotation of the hub will cause the needle engaging projections of the hub to follow the thread until the proximally facing annular surface of the hub contacts distally facing annular surface of the barrel to form primary seal between the hub and the barrel; the outwardly projecting annular sealing ring is positioned between the threaded projections and the proximal facing annular surface of the hub; and the needle assembly is installed or removed from the barrel by rotating the hub, and wherein the secondary seal is a backup seal in the event that the user fails to provide enough rotational torque while connecting the hub to the barrel to adequately engage the primary seal. an elongate syringe barrel having a longitudinal axis, an inside surface defining a chamber for retaining fluid, an open proximal end, an open distal end including a collar and a distally facing annular surface projecting inwardly from said collar, a portion of said collar having a cylindrically shaped, axially aligned circular side wall; a needle assembly including a hub having a body portion including a proximal end, a distal end, a conduit therethrough, a proximally facing annular surface on said body portion contacting said annular surface of said barrel forming a primary seal between said hub and said barrel, said hub further including an outwardly projecting annular sealing ring sealingly engaging said circular side wall of said collar forming a secondary seal between said hub and said barrel, said needle assembly further including a cannula having a distal end, a proximal end and a lumen therethrough, said proximal end of said cannula being connected to said distal end of said hub so that said lumen is in fluid communication with said chamber; and means for releasably engaging said hub to said collar including at least one thread on an inside surface of said collar or at least one thread on an outside surface of said hub, characterized by wherein distally facing annular surface of the barrel is flat and proximally facing annular surface of the hub is flat; two thread engaging projections on opposite sides of the hub; wherein during installation, rotation of the hub will cause the needle engaging projections of the hub to follow the thread until the proximally facing annular surface of the hub contacts distally facing annular surface of the barrel to form primary seal between the hub and the barrel; the outwardly projecting annular sealing ring is positioned between the threaded projections and the proximal facing annular surface of the hub; and the needle assembly is installed or removed from the barrel by rotating the hub, and wherein the secondary seal is a backup seal in the event that the user fails to provide enough rotational torque while connecting the hub to the barrel to adequately engage the primary seal.