Key, notably for a motor vehicle, comprising: - a casing with an upper half-shell forming a lid and a lower half-shell forming the casing bottom, - an insert (5, 7) mounted so that it can pivot with respect to said casing, in an axis of pivoting, between a rest position in which the insert (5, 7) is retracted or stowed in said casing and a position of use in which the insert (5, 7) is deployed out of said casing, - a mechanism for deploying the insert (5, 7) which is mounted in said casing and comprises: • a push-button housed axially in an associated housing of the upper half-shell and projecting with respect to the upper half-shell to be actuated by a user, and • an elastic return element for returning the insert (5, 7), a first end of which is connected to the insert (5, 7) to urge the insert (5, 7) to pivot towards said position of use when the push-button is actuated, the push-button comprising a means for blocking the rotation of the push-button with respect to said casing that forms a guide for the push-button in axial translation, said return element being fixed to the push-button by a second end, the insert comprising a key bit and a key bit support secured to the key bit mounted so that it can pivot with respect to said casing, the first end of said return element being fixed to said key bit support so that said return element urges said support to pivot with respect to said casing in order to deploy the key bit when the push-button is actuated, the key bit support comprising a hollow pin to house the first end of the return element at the end wall of the key bit support, said pin being connected to an internal side wall of the key bit support by a radial bridge, said lower half-shell of said casing having a recess to accept said key bit support in said rest position, an orifice being provided on the internal wall of said lower half-shell in the region of the recess into which said pin can be nested, the key comprising a means of halting the translational movement of the push-button which is situated at least partially in said support, said halting means comprising a stop post formed out of the lower half-shell and which enters a cavity provided in said support open at its bottom in the arc of a circle centered on the axis of pivoting so that as the support pivots, the stop post travels along the arc of a circle until the radial bridge comes into abutment against the stop post, so as to block the pivoting movement of the support. - a casing with an upper half-shell forming a lid and a lower half-shell forming the casing bottom, - an insert (5, 7) mounted so that it can pivot with respect to said casing, in an axis of pivoting, between a rest position in which the insert (5, 7) is retracted or stowed in said casing and a position of use in which the insert (5, 7) is deployed out of said casing, - a mechanism for deploying the insert (5, 7) which is mounted in said casing and comprises: • a push-button housed axially in an associated housing of the upper half-shell and projecting with respect to the upper half-shell to be actuated by a user, and • an elastic return element for returning the insert (5, 7), a first end of which is connected to the insert (5, 7) to urge the insert (5, 7) to pivot towards said position of use when the push-button is actuated, the push-button comprising a means for blocking the rotation of the push-button with respect to said casing that forms a guide for the push-button in axial translation, said return element being fixed to the push-button by a second end, the insert comprising a key bit and a key bit support secured to the key bit mounted so that it can pivot with respect to said casing, the first end of said return element being fixed to said key bit support so that said return element urges said support to pivot with respect to said casing in order to deploy the key bit when the push-button is actuated, the key bit support comprising a hollow pin to house the first end of the return element at the end wall of the key bit support, said pin being connected to an internal side wall of the key bit support by a radial bridge, said lower half-shell of said casing having a recess to accept said key bit support in said rest position, an orifice being provided on the internal wall of said lower half-shell in the region of the recess into which said pin can be nested, the key comprising a means of halting the translational movement of the push-button which is situated at least partially in said support, said halting means comprising a stop post formed out of the lower half-shell and which enters a cavity provided in said support open at its bottom in the arc of a circle centered on the axis of pivoting so that as the support pivots, the stop post travels along the arc of a circle until the radial bridge comes into abutment against the stop post, so as to block the pivoting movement of the support. • a push-button housed axially in an associated housing of the upper half-shell and projecting with respect to the upper half-shell to be actuated by a user, and • an elastic return element for returning the insert (5, 7), a first end of which is connected to the insert (5, 7) to urge the insert (5, 7) to pivot towards said position of use when the push-button is actuated,