The present invention relates to a fluid delivery assembly for a spraying apparatus. The assembly comprises an outer cup, a lid having a fluid outlet adapted to couple the lid to the spraying apparatus, and a liner for holding paint. The fluid delivery assembly comprises an interlocking keyed geometry adapted to prevent rotation of at least one of the lid and the liner with respect to the cup. The interlocking keyed geometry comprises at least one of (a) at least one protrusion of the cup extending into at least one recess of the lid, and (b) at least one protrusion of the lid extending into at least one recess of the cup, wherein the liner is trapped between the protrusion and the recess. The invention also relates to liners for such fluid delivery assemblies, which may be provided as a set of liners having different inners volumes.