A belt shaft housing (40) for a belt shaft of a seatbelt system comprises a shaft holder (42) for holding the belt shaft, a securing component (48) including a retaining portion (88), and at least one fixing element (74) that is configured to fasten the belt shaft within the shaft holder (42). The securing component (48) is fastened to the shaft holder (42) such that it can adopt an assembly position and a securing position, wherein the fixing element (74) is released in the assembly position and is secured to the shaft holder (42) in the securing position. Further, a belt shaft including a webbing, a belt pin and a sleeve-shaped axle is provided. There is moreover provided a belt tensioner, especially an end fitting tensioner, comprising such belt shaft housing (40) and such belt shaft as well as a method for assembling such belt tensioner.