How many centimeters of rock slab can be laid on the stair treads?

The stair tread can be paved with a rock slab with an outer edge of 2 cm. According to relevant public information, when laying rock slabs on stair steps, at least 2 cm should be reserved at the outer edge, mainly to ensure the beauty and safety of the whole staircase, but not more than 3 cm. The space of 2 cm is the most suitable, and the space size of the outer edge should be determined according to the design style and aesthetics of the whole staircase.