Coilable extendible member and methods

A method of manufacturing an extendible member which is configurable between a coiled form and an extended form, comprising:

• connecting at least one resilient secondary member to a primary member at first and second different circumferential positions on the primary member;
• wherein the primary member comprises a sheet of material resiliently biased to form a slit tube with a slit extending along its length, wherein the slit tube can be opened out at the slit to assume an open form in which it has a flattened cross section;
• wherein in the extended form, the primary member is in its slit tube form and the resiliency of the secondary member causes at least part of the secondary member to displace towards the slit in the primary member such that a continuous section of the secondary member curves towards and spans the slit to provide torsional and axial stiffness to the primary member;
• and
• wherein in the coiled form, the primary member is in its open form and the secondary member conforms to the flattened cross section of the primary member so that the primary and secondary members can be co-coiled.