[3DS MAX 2017] Bones stretchable like CAT Bones?

I’ve been getting back into porting to Garry’s mod and What-not. I’ve been wondering, the CAT bones allow you to stretch the bones into the position you like. And I want to know if it’s possible to do this with Bones (Like valve bones etc) I know using “INSERT” Turns on the Pivot mode, and it sorta works. But sometimes bones go crazy when I do this. (Fingers just go all over the place when I move any arm bones)