Astm A403 shine ma'aunin bututun bututun mai, yana nuna kayan aikin kayan na nau'ikan nau'ikan ƙarfe daban-daban, WP304 yana ɗaya daga cikin ƙarfe a wannan matsayin. 304 Wani nau'in baƙin ƙarfe na kowa, ana yin yalwa wajen kera kayan aiki da sassa wanda ke buƙatar cikakkiyar aikin kirki, juriya na lalata da kuma yin juriya.