Unfortunately Preway did fabricate unique chimney systems. Many were up to 11-inches in diameter and may be double wall systems. Anyway, measure the inside and outside diameter and note whether the chimney is single or double wall at the cap. Either a standard or custom fabricated cap can be ordered. For example (not endorsement), an 11-inch cap can be ordered here: http://www.fireplacemall.com/Chimney_Caps/Chim_Cap_Stainless_Forever_Rou/chim_cap_stainless_forever_rou.html

Thank you everyone