Patent ID: 7520147

Claim:
Anchorage device for fastening a counterweight to a washing machine tub comprising: an hollow shell ( 1 ) in which a concrete ballast mass ( 2 ) is adapted to be poured, said shell ( 1 ) being provided with fastening housings ( 3 ), and threaded fastening means ( 4 ) adapted to cooperate with said fastening housings ( 3 ) in order to secure said shell ( 1 ) to a washing machine tub ( 5 ), characterized in that said fastening housings ( 3 ) comprise expansion cavities ( 6 ) shaped so as to define an equivalent diameter ( 7 ), said threaded fastening means ( 4 ) comprise a head ( 8 ) integrally provided with a flange adapted to engage the tub ( 5 ) and a shank adapted to be screwed into said expansion cavities ( 6 ), said shank comprising a self tapping thread portion ( 9 ) having a crest diameter ( 10 ) and a root diameter ( 11 ) and a not-threaded pin portion ( 12 ) having a pin portion diameter ( 13 ), the ratio of the root diameter ( 11 ) of the self-tapping thread portion ( 9 ) to the equivalent diameter ( 7 ) of said expansion cavities ( 6 ) being in the range of about 1 to about 1.1, the ratio of the crest diameter ( 10 ) of the selftapping thread portion ( 9 ) to the equivalent diameter ( 7 ) of said expansion cavities ( 6 ) being in the range of about 1.1 to about 1.2, the ratio of the pin portion diameter ( 13 ) of the not-threaded pin portion ( 12 ) to the equivalent diameter of said expansion cavities ( 6 ) being in the range of about 1.3 to about 1.7.