Abstract: A scaffolding support assembly particularly useful as a base for modularized post-and-runner type scaffolding used on the interior of boilers or similar large interior spaces having sloping bottom walls when employed for inspection, repair, maintenance, etc. Such scaffolding support assembly preferably comprising a scaffolding post swivel base having pivotably attached thereto longitudinally adjustable stabilizing diagonals having a connector assembly at the free end of said diagonal for securing to a connector, preferably lower, on an adjacent scaffolding post. The resulting scaffolding system has unique versatility and ease in rapidity of assembly because the swivel bases rest on the sloping sides without attachment thereto, being stabilized in position by the adjustable diagonals.