These are the three horizontal studs in the rear that the mount slides over and into the center valley between the cases.
The nuts secure the mount to the rear of the case.

• Stud (3ea)-(24817-52) 3/8“x3-1/4” grade 5 zinc, case end is threaded 3/8“x16, nut end is threaded 3/8”x24.
• Nut (3ea)-(7775, Flexlock) 3/8“x24 or (7775NY, Nylock) 3/8”x24x9/16“.

These go in on the 'shelf' or top of the engine cases in the rear.

• 1957-1975 bolts: All
  • 3/8”x16x1-3/16“ parkerized, hex head.
    Part # (4348)
    57-66 XLH/XLCH & 67-69 XLCH (4 ea.)
    67-75 XL/XLH/XLS (2 ea.)
• L1970-E1975 studs:
  • L70-E72 XLCH
    1 bolt in the left side and a stud (24825-66) 3/8”x1-5/8“ parkerized in the right side.
    The case side is 3/8”x16, the other side is 3/8“x24.
  • L72-E75 XLCH
    1 bolt in the left side and a stud (24824-67) 3/8”x2“ grade 5 zinc in the right side.
    The case side is 3/8”x16, the other side is 3/8“x24.
• 1976 XLCH bolts :
  • 3/8”x16x1“ grade 5 zinc, hex head.
    Part # (2879W) (2 ea.)
    
• 1976-1978 XL/XLH/XLS bolts :
  • 3/8”x16x1“ grade 5 zinc, hex head
    Part # (2879W) (2 ea.)
• 1977-1978 XLCH bolts:
  • 3/8”x16x1-1/4“ grade 5 zinc, hex head
    Part # (4716W) (2 ea).
• 1979-1985 All, bolts:
  • 3/8”x16x1-1/4“ grade 5 zinc, hex head.
    Part # (4716W) (2 ea).

• 1957-1962:
  • 3/8”x24x1-1/8“ parkerized, hex head.
    Part # (4336) (2 ea).
  • Replacement in 63 was 3/8”x24x1-1/8“ grade 5 zinc, hex head.
    Part # (4336w) (2 ea).
• 1963-1972:
  • 3/8”x24x1-1/8“ grade 5 zinc, hex head.
    Part # (4336w) (2 ea).
• 1973-1978:
  • 3/8”x24x2-1/4“ grade 5 zinc, hex head.
    Part # (3945) (1ea).
  • 3/8”x24x1-1/8“ grade 5 zinc, hex head.
    Part # (4336w) (1ea).
• 1979-1981:
  • 3/8”x24x1-1/8“ grade 5 zinc, hex head.
    Part # (4336w) (1ea).
  • 3/8x24x3” grade 5 zinc, hex head.
    Part # (4415) (1 ea).
• 1982-E1983:
  • 3/8“x24x3-3/4” grade 5 zinc, hex head.
    Part # (3455) (2 ea).
• L1983-1985:
  • 3/8“x24x3-3/4” grade 5 zinc, hex head.
    Part # (3455) (1 ea).
  • 3/8x24x3-1/4“ grade 5 zinc, hex head.
    Part # (4434W) (1 ea).

• 1957-1960:
  • 3/8”x24x2“ grade 5 zinc, hex head.
    Part # (4380W) (2 ea).
• 1961-E1962:
  • 3/8”x24x2-1/16“ cad, hex head.
    Part # (4388B) (2 ea).
    (although JW Boon lists this as 2-1/8” long)
  • Replacement in 76 was 3/8“x24x2” grade 5 zinc, hex head.
    Part # (4380W) (2 ea) sold in 76 for 54-E62 models.
• L1962-1972:
  • 3/8“x24x2-1/2” parkerized, hex head.
    Part # (4452B - or HB) (2 ea).
  • Replacement in 76 was 3/8“x24x2-1/2” grade 5 zinc, hex head.
    Part # (4412) (2 ea) sold in 76 for L62-up models.
• 1973-1978:
  • 3/8“x24x2-1/2” grade 5 zinc, hex head.
    Part # (4412) (2 ea).
• 1979-E1983:
  • 3/8“x24x2-1/4” grade 5 zinc, hex head.
    Part # (3945) (2ea).
• L1983-1990:
  • 3/8“x24x3-1/2” grade 5 zinc, hex head.
    Part # (4435W) (2 ea).