| List - I | List -II |
| (Details of collar stud) | (Standard dimension) (Where 'd' is nomial diameter of stud) |
| (A) Threaded length of nut end | (I) d |
| (B)Diameter of collar | (II) 0.4 d |
| (C)Thickness of collar | (III) 1.5 d |
| (D)Length of metal end | (IV) 2 d+6 |
What comes next in the series?
\(2, 6, 12, 20, 30, \ ?\)