In the science fiction novels The Mote in God's Eye and The Gripping Hand by Larry Niven and Jerry Pournelle, the gripping hand is used literally to refer to the strongest of the three asymmetrical arms of the alien "Moties", some species of which have two weaker arms with better fine control on one side and a single much stronger arm on the other side.
It is used figuratively when presenting a third choice or fact after two others, usually after the second is presented with the phrase "on the other hand". (For the third choice, one could say "on the third hand", but the point here is, humans don't *have* a third hand.)
Thus, a discussion of choices could follow the typical English pattern of saying "We could do this, but on the other hand we could do that," followed by what would in conventional English be a non sequitur, "but on the gripping hand, there's another alternative. In keeping with the idea that this represents the strongest arm, the last choice is often the most unpleasant or difficult to deal with, or the strongest or most compelling.
Some of the more devoted fans of Niven and Pournelle will sometimes slip into this metaphor in regular speech, often resulting in some confusion for the listener. The abbreviation OTGH, modeled on OTOH, is also used in some SF discussion groups.