The ornamental design for strengthened block for folding camp chair, as shown and described.
FIG. 1 is a front perspective view of a strengthened block for folding camp chair showing my present design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a front elevation view thereof;
FIG. 7 is a rear elevation view thereof;
FIG. 8 is a front perspective view of the strengthened block for folding camp chair, shown at a reduced scale and showing how the strengthened block would appear on a folding camp chair; and,
FIG. 9 is a rear perspective view of the strengthened block for folding camp chair, shown at an increased scale and shown in more detail than section A of FIG. 8.
The broken lines are shown for illustrative purposes only and form no part of the claimed design