Adjustable support arm assembly

An adjustable support arm assembly comprising:

• a holder frame affixed to a support;
• a mounting frame for supporting an object,
• a link, and
• two coupling structures respectively coupling two distal ends of said link to said holder frame and said mounting frame, said coupling structures each comprising:
• a female coupling member, said female coupling member comprising two circular coupling holes axially aligned and a toothed portion extending around one end of said circular coupling holes;
• a male coupling member, said male coupling member comprising a transversely extending polygonal coupling hole disposed between the two circular coupling holes of said female coupling member;
• a polygonal shaft inserted through the circular coupling holes of said female coupling member and fitted into the polygonal coupling hole of said male coupling member, said polygonal shaft having a peripherally toothed head movable with said polygonal shaft between a locking position where said peripherally toothed head is engaged with the toothed portion of said female coupling member to lock said female coupling member to said male coupling member and an unlocking position where said peripherally toothed head is disengaged from the toothed portion of said female coupling member for allowing turning of said female coupling member about said polygonal shaft relative to said male coupling member;
• a cap fixedly connected to one end of said polygonal shaft opposite to said peripherally toothed head;
• and
• a compression spring mounted on said polygonal shaft and stopped between said cap and said female coupling member to support said polygonal shaft in said locking position.