What have you you bought?. if its a two winding choke on a common toroid core, then each winding will be about 10 mH, the mutual inductance between them will be 20 mH, so if you connect them the correct way around , you will get 40. If you connect them the wrong way around you will get zero. Or each winding could be 40 mH, giving 160 mH or nothing. Or they could be two isolated 40 mH chokes, which could give you 80 mH (in series ) or 20 (in parallel).
Frank