32.—(1) The size and shape of a stud incorporating reflectors or retroreflecting material shall be such that the part which is visible above the surface of the road can be contained within—
(a)an overall length in the direction of travel of traffic of not less than 35 millimetres and not exceeding 250 millimetres; and
(b)an overall width of not less than 84 millimetres and not exceeding 190 millimetres.
(2) No road marking or stud shall project above the surface of the adjacent carriageway more than 6 millimetres at any point except—
(a)a depressible stud, which shall not project above that surface more than 25 millimetres at its highest point, whether depressed or not;
(b)a non-depressible stud, which shall not project above that surface more than 20 millimetres at its highest point;
(c)the central circular part of the road marking shown in diagram 1003.4, which shall not project above that surface more than 125 millimetres at its highest point or 6 millimetres at its perimeter;
(d)the road marking shown in diagram 1012.2, the raised ribs on which shall project above the surface of the remainder of the marking by not more than 11 millimetres; or
(e)the road marking shown in diagram 1012.3, the raised ribs on which shall project above the surface of the remainder of the marking by not more than 8 millimetres; and
(f)the road marking shown in diagram 1049.1, the height of which above the surface of the adjacent carriageway shall be within the range of dimensions indicated on the second part of that diagram illustrating the cross-section of the marking.
(3) In this regulation, the expression “depressible stud” means a stud so fitted that the height by which it, or part of it, projects above the surface of the adjacent carriageway is apt to be reduced when pressure is applied to the stud from above; and “non-depressible stud” and “depressed” shall be construed accordingly.