This stiff knee uses an adjustable link to provide support at the end of a TAB in a situation that doesn’t allow running a suspension cable up higher in the tree i.e. the house is directly above the TAB. This pairs with a TAB that is below the TAB supporting the house and links the two together to remove some of the load. Most of the time the lower TAB can be a 1.25x6-C1. Reach out if you’re not sure what size lower TAB you should use.