[XeTeX] why does Latin Modern Mono have some stretch and shrink with XeTeX ?

[David Carlisle]

For latex at least I think the thing to do is amend tulmtt.fd in base
so that it has

\DeclareFontFamily{TU}{lmtt}{%
\hyphenchar \font\m at ne
\fontdimen3\font\z@%<<
\fontdimen4\font\z@%<<
}

with the two extra lines ensuring that these two font dimens are set to 0.

(If you try this with a latex 2017/01/01 release you need to remake
the format as it is input during format creation)

David