An adapter for coupling a pressurized gas container to a gas port of an appliance, the container having an externally threaded neck and a pierceable barrier element disposed within an axial lumen in the container's neck for sealing the container's interior, the adapter comprising: a first coupling arrangement comprising an internally threaded neck receptacle for screw-type coupling with the container's neck and having a gas port portion coupled to or being configured for coupling to a gas port of the appliance; a forwardly extending shaft configured to be received within said lumen and having a tip configured for piercing or rupturing the barrier upon screw-type engagement of the first coupling arrangement with said neck; a gas conduit within the adapter, comprising a shaft duct formed within said shaft, for gas communication between one or more openings proximal to the tip and said gas port portion; a plunger member displaceable within a cavity between disengaged and engaged positions and configured for blocking said first coupling arrangement from decoupling from the neck when in the engaged position, said cavity being in gas communication with said gas duct, such that gas pressure within the duct causes displacement of the plunger member to said engaged position; and a plug fitted within said gas port portion and being displaceable between a gas flow-blocking state, in which it blocks the flow of gas from the cavity to the gas port of the appliance, and a gas flow-permitting state, in which it permits flow of gas into the gas port of the appliance, the plug being axially switchable between the two states upon coupling of the adapter with the gas port and is biased to the gas flow-blocking state, characterized in that the plunger member is integral with said shaft and axially displaceable within an axial cavity between the disengaged and the engaged positions, said gas duct terminating at a rear end of the plunger member, a gas pressure formed at said rear end causes the plunger member to displace into the engaged position in which it applies a gas pressure-induced axial force on the container's neck lips, and a neck-facing face of the plunger member comprises an annular depression around the shaft, said depression being dimensioned for tight association with said neck lips in said engaged position of the plunger member. a first coupling arrangement comprising an internally threaded neck receptacle for screw-type coupling with the container's neck and having a gas port portion coupled to or being configured for coupling to a gas port of the appliance; a forwardly extending shaft configured to be received within said lumen and having a tip configured for piercing or rupturing the barrier upon screw-type engagement of the first coupling arrangement with said neck; a gas conduit within the adapter, comprising a shaft duct formed within said shaft, for gas communication between one or more openings proximal to the tip and said gas port portion; a plunger member displaceable within a cavity between disengaged and engaged positions and configured for blocking said first coupling arrangement from decoupling from the neck when in the engaged position, said cavity being in gas communication with said gas duct, such that gas pressure within the duct causes displacement of the plunger member to said engaged position; and a plug fitted within said gas port portion and being displaceable between a gas flow-blocking state, in which it blocks the flow of gas from the cavity to the gas port of the appliance, and a gas flow-permitting state, in which it permits flow of gas into the gas port of the appliance, the plug being axially switchable between the two states upon coupling of the adapter with the gas port and is biased to the gas flow-blocking state, characterized in that the plunger member is integral with said shaft and axially displaceable within an axial cavity between the disengaged and the engaged positions, said gas duct terminating at a rear end of the plunger member, a gas pressure formed at said rear end causes the plunger member to displace into the engaged position in which it applies a gas pressure-induced axial force on the container's neck lips, and a neck-facing face of the plunger member comprises an annular depression around the shaft, said depression being dimensioned for tight association with said neck lips in said engaged position of the plunger member.