Clamp used for small round head tensile sample machining

The utility model relates to the tensile sample machining, in particular to the small round head tensile sample machining. The utility model discloses a clamp used for the small round head tensile sample machining, which comprises a pair of collets; wherein each collet comprises a stretching section and a clamping section which are integrated as a whole; the excircle cambered surface of the clamping section is provided with a U-shaped groove along the axial direction of the clamping section; the circle center of the circular arc at the bottom of the groove coincides with that of the cross section of the clamping section; and the U-shaped groove is provided with a step with gradually largening diameter, so that the U-shaped groove is divided into a large diameter section and a small diameter section. The utility model can improve the machining efficiency of the small round head tensile sample, reduce the material consumption cost, and decrease unnecessary labor cost and equipment operation.