This route offers the walker an alternative means of travelling between Hartsop and Troutbeck from the more obvious and much easier route taken by Kirkstone Pass. The obvious reason for opting for the Threshthwaite Mouth route would be to avoid the traffic on the main road. I can understand why shepherds would have used Threshthwaite Mouth as a crossing point between the two valley heads, but I can't believe that anyone in the past would realistically view this as a more straightforward way of passing over from the two villages in question. Despite an element of doubt about it actually being classed as a pass, I've still included Threshthwaite Mouth because it has every feature expect to find on one. It's only downfall is that the Romans got here first and 'created' Kirkstone Pass a little further to the west.
On the Troutbeck side there are two choices of route. One on the west side of the valley which follows more of a straight line course, and the one I've chosen which may not be quite as straight, but it does link up with what is the more prominent track on the east side of Troutbeck Tongue.