Those are the only two lamp assemblies designed for use in a 6-cell, series parallel battery combination that the M6 uses.
However, if you remove 3 cells from the battery holder and use a volt meter to verify you are still at 9 volts (you will have to try various battery combinations until you get 9v) you can use these 9 volt lamp assemblies; N2, MN15 & MN16.
Some people run the above lamp assemblies on all 6 cells but this can/will lead to pre-mature failure of the lamps because they will draw too much current.
Hope that makes sense. /ubbthreads/images/graemlins/smile.gif