I agree with the others the single size seems to do equally well for both N and K frame revolvers.
Sorry for the peculiar revolvers that I use for modeling the adapter. I mostly have older guns.
Here it is on an old Triple Lock (N-frame).
And on a postwar K-38 Masterpiece:
Just for grins I tried it on a round butt K-frame, in this case a Model of 1902, first change.
The adapter is really quite comfortable on any gun I tried it on. I think Kip probably has a chance to sell several hundred of these over the next many months, and maybe even a few thousand once word starts to get around.
I had previously tested old Pachmayr and S&W grip adapters on some of my revolvers but didn't really like them. The non-metallic pieces just seemed too light and even subject to torquing on the frame if I really muscled my fingers into them. Kip's product seems stiffer, so even though it is still light and doesn't seem to displace as much volume as the aluminum version he seeks to replace, I find them preferable to the older molded adapters I have tried.
Maybe it's just my revolvers, but any adapter I have tried looks as though it would benefit from being custom shaved for a specific frame. In this case, Kip's K-N prototype actually seems to nestle against the trigger guard on the N frame a little better than it does on the slightly smaller frame, though the picture above doesn't seem to show that. It's a subjective feeling I get with the gun in my hand. But if I went through my entire safe, I bet I could find both a K and an N frame revolver that the adapter would fit without any adjustment whatsoever.