A support assembly is provided which is engageable to an as-used position in contact with opposing sidewalls of an air duct to stiffen and increase structural support. The device is engageable between parallel and non parallel sidewalls of ducts through the provision of a support member with pivoting ends configured to engage with the opposing sidewalls. The pivoting ends are in a reverse threaded engagement with opposing ends of the support member whereby rotating the support member will change the length of the assembly.
