What does Regulation 212 stipulate about legally required tread depth of tyres?

Regulation 212. Tyres

No person shall operate on a public road -

(a) a motor vehicle, other than a tractor or trailer, which is equipped with a metal tyre;
(b) a tractor or trailer, other than an animal-drawn vehicle, which is equipped with a metal tyre of less than 130 millimetres in width;
Prepared by: In partnership with:Page 234 of 378
(c) an animal-drawn vehicle which is equipped with a metal tyre less than 40 millimetres in width;
(d) a vehicle which is equipped with a metal tyre unless the whole width of the tread of the tyre is at all times in direct contact with the surface of the road;
(e) a vehicle which is equipped with a tyre which is in such a state of disrepair or in such a  condition that it may cause or is likely to cause damage to the road surface or may be or is likely
to be a danger;
(f) a motor vehicle which is equipped with a pneumatic tyre of which the rubber covering is so worn  or damaged that the fabric or cord used in the construction of such tyre is exposed;
(g) a motor vehicle of which a tyre is so constructed and fitted that the metal part of the wheel to which such tyre is fitted may come into contact with the road surface;
(h) a motor cycle which is equipped with a retreaded tyre;
(i) a motor vehicle which is equipped with a regrooved tyre having a bead diameter of 430  millimetres or less;
(j) a motor vehicle -
(i) which is fitted with a pneumatic tyre unless such tyre displays throughout, across its breadth and around its entire circumference, a pattern which is clearly visible, and has a tread of at least one millimetre in depth; or
(ii) which is fitted with a pneumatic tyre which contains a tyre tread depth indicator, if the  tread is level with the tyre tread depth indicator:

Provided that this paragraph shall not apply in respect of a motor cycle with an engine which  has a cylinder capacity not exceeding 50 cubic centimetres, or a trailer drawn by a tractor at a speed not exceeding 40 km/h;
(Regulation 212(j) amended by regulation 42(a) of General Notice 2116 of 2001)
(Regulation 212(j) amended by regulation 29(e) of Government Notice R404 of 2007)
(k) a motor cycle with an engine having a cylinder capacity not exceeding 50 cubic centimetres, which is fitted with a pneumatic tyre which does not at any position on the tread thereof have a visible tread pattern over at least 80 percent of the full width of the tread;
(l) a motor vehicle which is equipped with a pneumatic tyre which has a break in its fabric or which has a cut, measured in any direction on the outside of the tyre and of such depth that it reaches
Prepared by: In partnership with:Page 235 of 378 the cords used in the construction of such tyre, in excess of 25 millimetres or 10 percent of the maximum width of the tyre, whichever is the greater;
(Regulation 212(l) amended by regulation 7(a) of Government Notice R871 of 2005, as revoked and replaced by regulation 7(a) of Government Notice R891 of 2006)
(m) a motor vehicle which is equipped with a pneumatic tyre which has a lump or bulge caused by the separation of or a partial break in its structure.
(n) A minibus, midibus, or bus operating in terms of an operating licence issued in accordance with the provisions of the NLTTA, unless such minibus, midibus or bus is fitted with commercial steel
radial tyres;
(Regulation 212(n) added by regulation 7(b) of Government Notice R871 of 2005, as revoked and replaced by regulation 7(b) of Government Notice R891 of 2006)
(o) A minibus, midibus or bus operating in terms of an operating licence issued in accordance with the provisions of the NLTTA unless such minibus, midibus or bus is fitted with a vehicle directional stability control devise [sic].
(Regulation 212(o) added by regulation 7(b) of Government Notice R871 of 2005, as revoked and replaced by regulation 7(b) of Government Notice R891 of 2006 with effect from a date published by the Minister by
Notice in the Gazette)
(Regulation 212(o) substituted by regulation 15 of Government Notice R589 of 2009 with effect from a date to be determined by the Minister by notice in the Gazette)

Also view:

Tyre Safety and Road Safety

What does Regulation 212 stipulate about legally required tread depth of tyres?