Crossword puzzle clue "grid uniform part"

Grid uniform part

The 2x2 black square near the middle of this puzzle's grid, e.g., which is part of eight answers

Old rush participants ... or a three-part hint to what can be found in this puzzle's grid or clues

Part of a grid team

Part of many a grid

1967 Box Tops hit about part of a puzzle answer grid?

Part of a supermarket uniform?

Uniform part, maybe