The ornamental design for a flutemouthpieceendcap, as shown and described.
FIG. 1 is a front top perspective view of a flute mouth piece end cap showing the new design;
FIG. 2 is an exploded front top perspective view with the stone removed from the seating section of the flute mouth piece end cap thereof;
FIG. 3 is a side view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof; and,
FIG. 6 is a perspective view of a flute and the placement of the flute mouth piece end cap thereon.
The broken lines showing an inner surface of the flute mouth piece end cap of FIG. 5 and the broken lines showing of a musical flute instrument in FIG. 6 are for illustrative purposes and form no part of the claimed design.