Method and apparatus for making a contoured muntin bar assembly or grid. A tubular muntin bar grid has a first muntin bar formed from an elongated tube having ends that engage a window spacer frame and include side walls that have relatively narrow top and bottom planar walls and relatively wider side planar walls. The top and bottom planar walls defining one or more slots that define intersecting muntin bar positions. One or more intersecting muntin bars formed from elongated tubes have ends that engages the first elongated muntin bar in a region of a slot. The grid includes one or more joiner clips for positioning the one or more intersecting muntin bars in relation to said first muntin bar. Each joiner clip has a tree portion that extends into one end of said intersecting muntin bars to support the intersecting muntin bars in relation to the first muntin bar and an anchor portion which extends into a slot of said first muntin bar and connects to a wall of the first muntin bar spaced from a wall of the first muntin bar contacted by an associated intersecting muntin bar which engages the tree portion of the joiner clip. The anchor portion includes either an integral tab which traps the wall of the muntin bar between a flexible finger or a separate tab which is mounted to a clip base that defines the flexible finger.