PART NO.  SPL.PAGE  DESCRIPTION                                                           
CHS2510   16.N.11   Stud - plinth to body (4) -(stop/tail, road lamps, 1600-MK-II)-
    Com.(C)101352

CHS2510 - Stud - for Tail light plinth to body -(1600-MK-II and1600-MK-II "Deluxe" cars)
High strength stud (55-ton).
Length = 1-1/4"
Top end thread = 5/16-24-UNF x 5/8"
Bottom end thread = 5/16-18-UNC x 15/32"
Notice that original CHSxxxx studs have short dog point on top end, which males it very easy to start the nut.
A leading "0" means plain stud. -- A leading "2" means zinc plated.