(1) W1--screw, head hoop and steel belt are made of galvanized iron
(2) W2--screw is made of galvanized iron, head hoop and steel belt made of stainless steel
(3) W4--screw, head hoop and steel belt are made of stainless steel
(4) W5--screw, head hoop and steel belt are made of 316 stainless steel