German industrial filter maker Mann + Hummel has agreed to buy U.S. peer Affinia (AFN.N) to boost its annual sales by $1 billion – or by more than a third – and gain access to the American market for heavy-duty and hydraulic filters. Privately-held Mann + Hummel said it would not disclose the terms, but a regulatory filing by Affinia showed the purchase price was $513.1 million. The German firm will also take on debt from Affinia, which stood at $822 million at the end of June.