PART NO.  SPL.PAGE  DESCRIPTION                                                           
52K487    15.F.1    Stud - gearbox extension (1) - Fin.(G)A915 - 
52K487    15s.F.1   Stud - gearbox extension (1) - Fin.(G)A915 - 
CHS2513   15.F.1    Stud - gearbox extension (2) -(GB casing, GB assy, 1500) -Com.(G)A916
CHS2513   15s.F.1   Stud - gearbox extension (2) -(GB casing, GB assy, 1500) -Com.(G)A916
CHS2513   16.F.1    Stud - rear extension (2) -(GB casing, GB assy, 1600 and 1600-MK-II)
CHS2513   TC.A.12   Stud for ehaust manifold (6) -(cyl.head, valves, engine, Twin Cam)
CHS2513   TC.F.1    Stud gearbox extension (2) -(gbx.casing, gearbox assy, Twin Cam)

CHS2513 - Stud -For gearbox casing extension (1 or 2) -(gearbox 1500, 1600, 1622, early 1800)
Also used for Twin Cam exhaust manifold
High strength stud (55-ton).
Length = 1-5/8"
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.

(2) pieces required for later gearboxes.
Part number was 52K487 (1 piece only) for early 1500 gearbox