Any matter admitted under this rule is conclusively established unless the court on motion permits withdrawal or amendment of the admission. The court may permit withdrawal or amendment when the presentation of the merits of the action will be subserved thereby and the party who obtained the admission fails to satisfy the court that withdrawal or amendment will prejudice that party in maintaining an action or defense on the merits. Any admission made by a party under this rule is for the purpose of the pending action only and is not an admission by the party for any other purpose nor may it be used against him in any other proceeding.