Handguard for clamping mounting on an existing firearm, in particular on its barrel or its barrel nut, the barrel or the barrel nut having an annular groove, comprising: - a shaft housing with a shaft axis, which has a slit running radially thereto and a through-opening running in the transverse direction for a clamping device, - a clamping device for the shaft housing, comprising ∘ a lever having a center element which surrounds the lever axis and lies in a through-opening of the shaft housing in a normal plane with respect to the shaft axis, and which has a recess in its center area, a thread at one end portion and a lever arm at the other end, and ∘ a nut with an internal thread matching the thread; whereby the center element is provided at its end portion directed towards the lever arm with a clamp taper socket widening towards the lever arm and contacts a conical clamping surface of the shaft housing; whereby, in the assembled state, the nut is screwed onto the thread and thus narrows the slit, and the angular position of the lever about its lever axis is such that its center element contacts the annular groove, characterized in that, the nut is provided on its outer side with a conical area, a clamp taper socket, in that, in the shaft housing, the through-opening for receiving the center element is a long hole with an outline comprised of two semicircles with a first axis and a second axis parallel thereto and a rectangle located in-between, and in that the long hole is provided on both ends with conical clamp surfaces, which are centric around the first axis and co-operate with the clamp taper sockets (22, 282). - a shaft housing with a shaft axis, which has a slit running radially thereto and a through-opening running in the transverse direction for a clamping device, - a clamping device for the shaft housing, comprising ∘ a lever having a center element which surrounds the lever axis and lies in a through-opening of the shaft housing in a normal plane with respect to the shaft axis, and which has a recess in its center area, a thread at one end portion and a lever arm at the other end, and ∘ a nut with an internal thread matching the thread; ∘ a lever having a center element which surrounds the lever axis and lies in a through-opening of the shaft housing in a normal plane with respect to the shaft axis, and which has a recess in its center area, a thread at one end portion and a lever arm at the other end, and ∘ a nut with an internal thread matching the thread; whereby the center element is provided at its end portion directed towards the lever arm with a clamp taper socket widening towards the lever arm and contacts a conical clamping surface of the shaft housing; whereby, in the assembled state, the nut is screwed onto the thread and thus narrows the slit, and the angular position of the lever about its lever axis is such that its center element contacts the annular groove, characterized in that, the nut is provided on its outer side with a conical area, a clamp taper socket, in that, in the shaft housing, the through-opening for receiving the center element is a long hole with an outline comprised of two semicircles with a first axis and a second axis parallel thereto and a rectangle located in-between, and in that the long hole is provided on both ends with conical clamp surfaces, which are centric around the first axis and co-operate with the clamp taper sockets (22, 282).