To improve a mold screw of a molding machine that a surrounding breach line of a nylon fastener does not expose over an element and a groove can be formed on the nylon fastener.

The groove is formed on a side element of nylon and a projection is formed below it. As the groove and the projection correspond to each other, a sewing machine string can be introduced to the groove and the string does not expose over the element. The projection moves the core wire in the element to both sides and let the connection tight. At the mold screw groove bottom in the nylon fastener former, a few arch-shape projections are provided. By way of the arch-shape projections, the nylon element are pushed and the groove is formed on the element and the projection is formed below it.