Wear part (3-7, 8, 9) for a bucket to a loading or digging machine, which bucket is provided with at least one front edge plate (10,11,12) with a forwardly directed engagement edge, wherein the wear part (3-7, 8, 9) has a forward direction (F) and a rearward direction (B) and is provided with a hook portion (16) for fixing of the wear part to the bucket, wherein the fastening portion has a spanning surface portion (20) for co-operating in a contact surface area with a clamping surface portion (19) on a fastening unit (13) which is positionable through a hole in said front edge plate. The spanning surface portion (20) extends at an angle α against said forward direction such that, in use, when tightening said fastening unit (13) a force effecting the wear part (3-7, 8, 9) in the rearward direction (B) will occur. The invention also concerns a fastening unit therefore and a wear part system, a bucket and a loading or digging machine.