Apr 02, 2018 · (3) A non-depressible stud must not project more than 20 mm above the surface of the carriageway. (4) Paragraph (5) applies to a stud which, in accordance with these Regulations, is fitted with reflectors, retroreflecting material, a light source or a combination. (5) The part of a stud which is visible when the stud is in place must have—