Many stainless steel alloys have a high enough iron percentage to attract a magnet, so if the frame attracts a magnet it could still be stainless. For example, my Reynolds 953 stainless frame attracts a magnet, albeit somewhat weaker than plain carbon steel, chromoly, or mangalloy. The chemical composition of 953 is ~75% Fe.



If the frame is older than 2006 vintage (953 was introduced in 2006 and XCr and KVA stainless were introduced after 953) and is indeed stainless, it would probably be Columbus Metax which was introduced in the 1990s.