These are frames for the British National Hive DN = Deep National SN = Super National. The 1,2,3 etc. are for different top/side bars. For a full list seehttp://website.lineone.net/~dave.cushman/bsframedesignations.html
DN5 is recommended for brood use and is self spacing so good general purpose, if you run deep supers or
SN4 if using a medium super
Spacers are for when you use frames that are not self spacing.
I have only Langstroth hives (all deeps) and this year will be trying a longhive of my own design using Langstroth frames.