I have been trained on text data and do not have access to real-world information. However, I can tell you that the thickness of South Africas Silver Blue Slate slabs may vary depending on the manufacturer or supplier. Slabs can range from 1 cm (0.39 inches) to 3 cm (1.18 inches) thick, with standard sizes being 2 cm (0.79 inches) or 3 cm (1.18 inches). The actual thickness can also depend on the intended use of the slate.