Apparatus is provided including an implant structure (22, 500), which includes a contracting mechanism (40), which comprises a rotatable structure (46, 810, 936), arranged such that rotation of the rotatable structure (46, 810, 936) contracts the implant structure (22, 500). A longitudinal member (86) is coupled to the contracting mechanism (40). A tool (80) for rotating the rotatable structure (46, 810, 936) is configured to be guided along the longitudinal member (86), to engage the rotatable structure (46, 810, 936), and to rotate the rotatable structure (46, 810, 936) in response to a rotational force applied to the tool (80). Other applications are also described.
