If you are using Old bolting then what you are getting for item 12 is a standard bolt (item 13) plus 38mm for the blind + 3mm (i assume this is gasket thickness).
For item 14 you get a standard bolt (item 15) plus 18mm for the blind + 3mm
My instinct to get the exact bolt length you are looking for is to change the blind thicknesses in the catalogue by 1mm.
In the overall scheme of things, 1mm will not make a significant difference. Especially when you take manufacturing tolerances into account.
Actually I've tried to change SB thickness from 18 -> 17.9, ..., 17.2, 17.1
The bolt len in Isome drops on DTAB (170mm) when the SB thick. is less than 17.5mm
(if I set SB thick greater than 17.5mm, Isome will come out value 18 for SB)
but the MESC doesn't come out until I set SB thickness 17mm.
this time, the bolt len & MESC come out as i hope.
But, again, the problem is my boss doesn't accept it while he checks Isometric,
because he said the SB thickness is wrong, and the worker might confuse that.
(he means SB thick = 17mm)
