A holder for clamping flexible sheet material includes an extruded plastic, elongated channel member having a base wall having two ends. The base wall is connected at one of the ends to a relatively short, upstanding forward leg having an inner face forming a bearing surface. The forward leg has a free upper end, and the base wall is connected at the other of the ends thereof to a relatively long, upstanding rearward leg having an upper end, and a top wall is joined to the upper end of the rearward leg. The top wall extends down behind the forward leg and has a free end which resiliently engages the bearing surface of the forward leg and it also has a crease or bend line spaced apart from the upper edge of the forward leg so as to define a wedge-shaped opening therebetween.