I just got it today, so I played around with different knives in it (Puma German stockman, Buck 301, Buck 055, Saunter, Case med Stockman, large Stockman, Sowbelly, large Trapper). They all fit!
The leather allows for larger profiles to fit, but being new it has not stretched out. The Buck 301, 055, Saunter with fob, and Puma are able to extract with the slip staying attached to the kangaroo pouch pocket of my hoodie. My Trapper has a clip so it is a little larger. I am waiting on a Kershaw Federalist to show up which will have a fob as well. I think the slip will break in to whichever knife I decide to carry in it most.
The Horsewright slip that attaches to a belt or belt-loop is awesome, but I wanted to try this out for keeping the blade in a set position, or in a shirt/hoodie/jacket pocket. Could also wear the slip on outside if doing a chore to have quicker access to it.