Apparatus for use with a guidewire is provided, the apparatus including (1) a first housing, shaped to define a first channel through which the guidewire is slidable； (2) a second housing, shaped to define a second channel through which the guidewire is slidable in at least a first direction toward the first housing； (3) a guidewire-engaging element, disposed within the second housing, and configured to inhibit the guidewire from sliding through the second channel in a second direction away from the first housing； and (4) a tubular member, (a) shaped to define a lumen therethrough, through which the guidewire is slidable, and (b) coupled to the second housing and slidably coupled to the first housing. Other embodiments are also described.
