A word in between "lesser" and "greater"

In many game systems (particularly fantasy or role-playing games), relative qualities or power levels are denoted by naming things using "lesser" or "greater". For example, in Dungeons and Dragons 3.5, there are weapon augmentation crystals, that might be named

• Least crystal of Arcane Steel
• Lesser crystal of Arcane Steel
• Greater crystal of Arcane Steel

etc.

It seems odd to me that there is a "least", a "lesser", and a "greater", but nothing in the middle. It makes sense that a "lesser" object is lesser than the "greater" one, and vice versa, but it seems strange to not have something in the middle. Of course one could argue that the one in the middle needs no such qualifier, but I was wondering - is there a word that can stand alongside words such as "lesser" and "greater" to denote that something is the "regular" version?

I thought of "common", but that strays into ideas of rarity, which is slightly different.

I think you are right when you say that it could be argued that 'the one in the middle' needs no qualifier. And that is likely what would be best. However, if you felt the need to emphasize its 'normality', so to speak, then I believe words such as standard, common, everyday, normal, conventional, or ordinary would suffice.