Abstract: A grid keying fixture for installing grid keys in a nuclear fuel assembly spacer grid having a matrix of cells, at least some of the cells including a soft stop in a first axis and a soft stop in a second axis. The grid keying fixture includes a frame assembly having a plurality of fixture pegs affixed to the frame assembly and each arranged and adapted to enter a respective cell of the grid. Each of the fixture pegs is operable to simultaneously deflect the first axis soft stop and the second axis soft stop of the respective cell without bearing on a hard stop in the respective cell opposite one of the first axis and second axis soft stops. In the preferred embodiment, alignment pegs are affixed to the frame assembly for aligning the fixture pegs with the respective cells.