In M6 x 1 6g and M6 x 1 6h thread gauges, 6g & 6h are the two different tolerance class for M6 thread. Normally 6g gauge is used for without plated thread and 6h gauge is used for plated thread,(if specific criteria is not mentioned).
6mm bolt with 1.0 thread pitch
The 2007 BMW M6 has a 5.0 L base engine size.
The 2008 BMW M6 has a 5.0 L base engine size.
The 2009 BMW M6 has a 5.0 L base engine size.
The 2013 BMW M6 has a 4.4 L base engine size.
The 2014 BMW M6 has a 4.4 L base engine size.
The 2006 BMW M6 has a 5.0 L base engine size.
The 2010 BMW M6 has a 5.0 L base engine size.
The 2014 BMW M6 has a V8 engine.
The 2008 BMW M6 has a V10 engine.
The 2013 BMW M6 has a V8 engine.