To place two or more parts into a grid on an ungridded sheet, select the Box Grid option and then drag out a box around the parts to be gridded (image 1), left-clicking to finalize the box grid. Image 2 shows the red bounding box that encloses the gridded parts. In this manner an entire sheet (of similar parts) can be re-gridded if the grid was cleared earlier.
Note: Similar parts must be evenly spaced in the X and Y for this option to take affect. Parts may have already been gridded to obtain the precise spacing required between parts; however, after initial gridding the grid must be converted to individual parts.
See Auto Grid and Grid for more info.