For C&C, the safe bar gaps would be 1.5". Anything bigger than that is too big and the piggies heads get stuck. Some brand of grids are not safe for building cages. Safe grids are 9x9 squares across. Some brands come in 8x8 or 5x5 squares across. Each grid is 14x14 inches.
Edit to add: 1.5" gap is too wide for babies. If you have babies, you'd have to overlap the grids to make the space smaller.