In reply to Franco Cookson:
> Thanks. Any other size 1 walnut beta much appreciated in the mean time..
As Deadeye posted 7 kN in an ideal placement. This is rated strength so you may be lucky and get a slightly better result.
In a fold back the wire will be bent possibly more harshly in a tighter radius, so weaker. It will also be compressed between the rock and the nut, this will probably have a significant weakening effect.
The angle the nut jams across the hole will have a significant effect on the holding power or the stress on the rock. It is not a predictable constant camming angle like a manufactured camming unit. and will exert a point load on part of the rock, which may be close to the rock face and thus prone to exploding the rock.
The strongest option in a pre drilled hole is to glue in a piece of metal ... Oh hang on a sec