The retro-fit mounting bracket is used to attach 220mm or 100mm plastic duct to existing duct mounting iron work. It is used when an extension is required to position ducting or when iron work cannot be moved. This kit suits both 5/8" UNC (16mm) and 1/2" UNC (12mm) rods, which are available separately. However, nut sets should be ordered separately; dependent on the size needed (½" UNC nut set is Part No: TC1279-17A. & 5/8" UNC nut set is Part No. TC1279-18A) Metric rods e.g. M12 or M16 are also available.