Spout assembly comprising: - a spout for a thin-walled flexible packaging, having a tube; - a closing assembly applicable to the spout, comprising: A) a cap comprising: an annular side wall, extending along a main axis between a lower edge and an upper edge, internally threaded, a base which closes it at the top, connected to the upper edge, and a cap flange, protruding radially externally from the side wall at the lower edge; B) a connecting device comprising: i) a connecting element or ring adapted to be axially constrained to the spout and freely rotatable about the tube of the spout, wherein said ring comprises an inner side surface and an outer side surface; ii) a plurality of breakable bridges joining the ring to the cap, suitable for tearing due to relative axial separation between the ring and the cap; iii) a connecting band or strap which joins the ring to the cap, characterised in that said strap has a predominant length with respect to the other dimensions, extends from a ring end joined to the outer side surface to a cap end joined to the cap and has, in an initial configuration in which the bridges are intact, a ring section projecting radially from the ring end, a cap section extending radially from the cap end, and a connecting portion which joins the cap section and the ring section; wherein - the spout has a connection seat to accommodate at least partially the ring, separated from the tube by an upper flange having a truncated cone-shaped outer lateral surface; and - the inner side surface has an inner projection configured to snap-fit with the upper flange and enter the connection seat. - a spout for a thin-walled flexible packaging, having a tube; - a closing assembly applicable to the spout, comprising: A) a cap comprising: an annular side wall, extending along a main axis between a lower edge and an upper edge, internally threaded, a base which closes it at the top, connected to the upper edge, and a cap flange, protruding radially externally from the side wall at the lower edge; B) a connecting device comprising: i) a connecting element or ring adapted to be axially constrained to the spout and freely rotatable about the tube of the spout, wherein said ring comprises an inner side surface and an outer side surface; ii) a plurality of breakable bridges joining the ring to the cap, suitable for tearing due to relative axial separation between the ring and the cap; iii) a connecting band or strap which joins the ring to the cap, characterised in that said strap has a predominant length with respect to the other dimensions, extends from a ring end joined to the outer side surface to a cap end joined to the cap and has, in an initial configuration in which the bridges are intact, a ring section projecting radially from the ring end, a cap section extending radially from the cap end, and a connecting portion which joins the cap section and the ring section; wherein A) a cap comprising: an annular side wall, extending along a main axis between a lower edge and an upper edge, internally threaded, a base which closes it at the top, connected to the upper edge, and a cap flange, protruding radially externally from the side wall at the lower edge; B) a connecting device comprising: i) a connecting element or ring adapted to be axially constrained to the spout and freely rotatable about the tube of the spout, wherein said ring comprises an inner side surface and an outer side surface; ii) a plurality of breakable bridges joining the ring to the cap, suitable for tearing due to relative axial separation between the ring and the cap; iii) a connecting band or strap which joins the ring to the cap, characterised in that said strap has a predominant length with respect to the other dimensions, extends from a ring end joined to the outer side surface to a cap end joined to the cap and has, in an initial configuration in which the bridges are intact, a ring section projecting radially from the ring end, a cap section extending radially from the cap end, and a connecting portion which joins the cap section and the ring section; wherein i) a connecting element or ring adapted to be axially constrained to the spout and freely rotatable about the tube of the spout, wherein said ring comprises an inner side surface and an outer side surface; ii) a plurality of breakable bridges joining the ring to the cap, suitable for tearing due to relative axial separation between the ring and the cap; iii) a connecting band or strap which joins the ring to the cap, characterised in that said strap has a predominant length with respect to the other dimensions, extends from a ring end joined to the outer side surface to a cap end joined to the cap and has, in an initial configuration in which the bridges are intact, a ring section projecting radially from the ring end, a cap section extending radially from the cap end, and a connecting portion which joins the cap section and the ring section; wherein - the spout has a connection seat to accommodate at least partially the ring, separated from the tube by an upper flange having a truncated cone-shaped outer lateral surface; and - the inner side surface has an inner projection configured to snap-fit with the upper flange and enter the connection seat.