Mix thoroughly margarine, sugar and vanilla. Sift together and stir in flour, and salt. Mix in nuts. Chill dough overnight. Roll into 1 inch balls (slightly smaller than a walnut). Place on ungreased cookie sheet. Bake at 400 degrees for 10 to 12 minutes, until set but not brown. Roll in powdered sugar while still warm and roll again when cool. Makes 8 dozen.