A Metal Duct Joiner is used to join two pieces of duct that are the same size. The ducting will simply fit over the joiner and will need to be taped or clamped in place

Ducts should be well supported to avoid joints being pulled apart or damaged.  It is not just the duct core that needs to be secured the insulation material used as duct insulation also requires securing, in this case you may use duct tapes and duct straps.