The ornamental design for a snaphookattachment for a firearm, as shown and described.
FIG. 1 is a left, front, top perspective view of snap hook attachment for a firearm attached to a firearm showing my new design;
FIG. 2 is a right, front, top perspective view of the snap hook attachment for a firearm of FIG. 1;
FIG. 3 is a left side elevation view of the snap hook attachment for a firearm of FIG. 1, the right side elevation being a mirror image;
FIG. 4 is a top plan view of the snap hook attachment for a firearm of FIG. 1; and
FIG. 5 is a bottom plan view of the snap hook attachment for a firearm of FIG. 1.
FIG. 6 is a front elevation view of the snap hook attachment for a firearm of FIG. 1; and,
FIG. 7 is a rear elevation view of the snap hook attachment for a firearm of FIG. 1.
The broken lines showing portions of the design in all figures are included for the purpose of illustrating environment and unclaimed features and form no part of the claimed design.