Pivot shaft assembly for a foldable device

A pivot shaft assembly for a foldable device, comprising:

• a pivot base including a base seat, an axial hole which extends through said base seat in a first direction, and a fastener releasing portion which is disposed on said base seat;
• a shaft member extending along a central axis through said axial hole, said shaft member including a fixed tubular piece which extends through said axial hole and which has a fixed tubular wall surrounding the central axis, and a movable tubular piece which is movably disposed within said fixed tubular piece and which has a movable tubular wall surrounding the central axis, said fixed tubular piece being pivotably coupled with said base seat about a rotating axis which is transverse to the central axis, said fixed tubular piece having a retreated hole which extends radially relative to the central axis through said fixed tubular wall, said movable tubular piece having a through hole which extends radially relative to the central axis through said movable tubular wall;
• and
• a fastening member disposed within said movable tubular piece, said fastening member having an engaging protrusion which resiliently projects from said through hole and which has an engaging end disposed outwardly of said through hole, wherein, when said pivot shaft assembly is in a fastened state, said shaft member is inclined relative to the first direction by a predetermined inclined angle, said retreated hole of said fixed tubular piece is remote from said fastener releasing portion, said through hole is aligned with said retreated hole, said engaging protrusion extends through said retreated hole to have said engaging end be outwardly of said retreated hole such that said movable tubular piece is not movable relative to said fixed tubular piece, and wherein, during shifting of said pivot shaft assembly to a releasable state where said shaft member extends parallel to the first direction, said engaging protrusion abuts against and is pressed by said fastener releasing portion along with rotation of said shaft member relative to said base seat to bring said engaging end to be retreated into said retreated hole so as to permit movement of said movable tubular piece relative to said fixed tubular piece.