Adjuster assembly

A piston assembly for engaging two selectively engageable parts comprising:

• a housing defining a piston cylinder;
• a piston;
• and an adjuster assembly comprising:
• a piston stroke limiter configured to limit the length of a return stroke of the piston from an extended stroke position and a retracted stroke position, the piston stroke limiter comprising a spring and a spring guide;
• and an inner crushable tube, acting between the piston and the piston stroke limiter, the inner crushable tube being arranged to reduce in axial length when a length of an extension stroke exceeds a length of a retraction stroke to maintain the length of the return stroke;
• wherein the inner crushable tube comprises an inner crushable thin-walled tube surrounding at least a portion of the piston, the adjuster assembly further comprising an outer crushable tube mounted around and radially outwards of the inner crushable tube on a tube support, an end of the tube support connected to an end of the inner crushable tube, the inner and outer crushable tubes configured to each form a crushed body of reduced axial length compared to the axial length of the tube when a predetermined force is applied to the tube.