A branch attachment is where a branch is attached to the trunk of a tree. Three types of branch attachment are recognized due to differences in the anatomical position of buds that form them. Two key components contribute to the mechanical strength and toughness of the attachment: interlocking wood grain at the top of the attachment and an embedded knot that often lies within the attachment. A common malformation of a branch attachment is the inclusion of bark within the join, which can weaken the attachment.