If a 340 has a $b, it maps to bf:Instance/bf:dimensions in marc2bibframe2. In bibframe2marc, that path maps to 300$c.
If a 340 has a $i, it maps to bf:instance/bf:systemRequirements/bf:SystemRequirements/rdfs:label. However, there is no mapping back to $i in bibframe2marc.
There's no mapping for $h and $1, both of which are rarely used.
If a 340 has a $b, it maps to bf:Instance/bf:dimensions in marc2bibframe2. In bibframe2marc, that path maps to 300$c.
If a 340 has a $i, it maps to bf:instance/bf:systemRequirements/bf:SystemRequirements/rdfs:label. However, there is no mapping back to $i in bibframe2marc.
There's no mapping for $h and $1, both of which are rarely used.