Same with the grips from Ruger, they are thick also. On Altamont's website they call them "classic". My single ten came with "gunfighter" grips, I think that's the same as what Altamont calls "slim".I'm a little different. I've ordered two different set of grips from Altamont. While they look terrific, they are thicker than I like. The original black plastic grips work for me.
I've been wanting to get a set (or three) of Altamont "slim" grips, but the ones I want have been "out of stock" for the last 3+ months.