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 . - 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 . <EOS>