A reinforcing member (36) for a belt shaft (10) comprises an elongate central portion (46) and two hooking portions (48) provided at the ends of the central portion (46) adapted to be hung into a hooking slit of a belt shaft body (28) of a belt shaft (10), wherein the central portion (46) includes a retaining portion (50) adapted to be encompassed by the webbing (26) and a supporting portion (58) extending in the longitudinal direction (L) substantially over the entire central portion (46) and being offset relative to a plane (M) which is defined by the retaining portion (50), and wherein retaining lands (60) defining a passage window (62) for the webbing (26) extend between the supporting portion (58) and the retaining portion (50). The invention further provides a belt shaft (10) comprising a belt shaft body (28) as well as an end fitting tensioner (12).