The ornamental design for a gridbar for modular fixturing, as shown and described.
FIG. 1 is a fragmented top perspective view of a grid bar for modular fixturing;
FIG. 2 is a front end view thereof the opposite side being identical;
FIG. 3 is a fragmented top plan view thereof, the bottom plan view being the same as the side shown; and,
FIG. 4 is a fragmented right side elevational view thereof, the left side elevational view being the same as the side shown.
The broken line showing of grooves and functional apertures are for illustrative purposes only and form no part of the claimed design. The claimed design is shown broken away to indicate indeterminate length.