PART NO.  SPL.PAGE  DESCRIPTION                                                           
53K249    15.A.7    Stud -L/H side crankcase blanking plate (2) [Fin(E)GB706]
53K257    15.A.7    Stud -L/H side crankcase blanking [Com(E)GB707 Fin(E)GB51767]
53K257    sup.1     Stud -petrol pump blanking plate (2) -(block assy, engine unit, sup)
53K257    16.A.1    Stud -crankcase vent pipe clip (2) -(block assy, engine unit, 1600)
53K257    16.A.21   Stud -crankcase vent pipe clip (2) -(block assy, engine unit, 1622)-
    Correction was [53H275
53K257    TC.A.1    Stud for plate (2) -(fuel pump port, cyl.block assy, engine, Twin Cam)

53K249 - Stud - for blanking plate, vent pipe clip (2) side of engine block -(1500, 1600, 1622, Twin Cam, 1800)
Length:1-1-4"
Top end thread: 5/16-24-UNF x 5/8"
Bottom end thread: 5/16-24-UNF x 15/32"

High Strength Stud
Fine thread both ends.

Note:53K249 and 53K257 appear to be identical parts. The part number changed when in late 1500 production the blanking plate was deleted with non-machined fuel pump port. It changed from 2 studs to 1 stud at that time (for the 1500 only), then back to 2 studs for later engines. But that doesn't explain the change of part number. It may have been intended tohave a shorter stud when the plate was deleted, but then there is a spacer washer for the breather pipe clip. In any case, the stud doesn't have to be shorter, so it looks like they just continued with the same length.