The ornamental design for an arm for spectacles, as shown and described.
FIG. 1 is a front elevational view from an external side of an arm for spectacles according to the present design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a rear elevational view from an internal side thereof;
FIG. 4 is a front perspective view from the top right thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a right side elevational view thereof; and,
FIG. 7 is a perspective view of a pair of arms for spectacles according to the present design, in orientation with the arm for spectacles (drawn with broken lines).
The broken lines shown in the drawings illustrate portions of a pair of spectacles in orientation with the present arm for spectacles that form no part of the claimed design.
The diagonal lines depict the surface appearance of the arm for spectacles.