Snap Dragon DoublesDefinition 1 From Granovetter's Conventions at a Glance. After a competitive auction where the LHO opponent opens, partner overcalls and RHO responds a new suit, a double would show the 4th suit (at least 5) and support for partner (usually 3, but could be honor doubleton). Of course, the snap dragon doubler is not expected to have many hcp. Examples: LHO part RHO you 1H 1S 2C x Showing diamonds and spade support 1S 2C 2D x Showing hearts and club support 1S 2C 2D 2H DENIES club support (else snap dragon) 1S 2C 2D 3C tends to deny having hearts Definition 2. From Tiger Bridge, relayed via email from Stephen Li. According to Tiger Bridge (a book from an English bridge expert, published in the late sixties) on the convention : Snap Dragon Double:, it is similar to what you published but quite different in objective. In his way of describing : LHO opened - partner overcalled with a MAJOR SUIT - RHO bid beyond the TWO level of LHO's opening suit - my Double is Snap Dragon Double. Partner passes if LHO bid or rebid his major suit to show minimum overcalling. Note the conditions are slightly more restrictive than the one you described. It showed 9+ points up with at least game invitational hands for partner's bid suit. This way, with limited values in my hand (8+ to 12), it immediately clarified whether the partnership is competing for partscore or not while it allows for partnership to overcall light. With game forcing hands and FIT (11+ up), my double immediately assessed the slam potentials when partner may have overcalled light and still have confidence for slam bidding. In my opinion, this approach is superior in practice in that It is important to let partner know how to bid on when fit is confirmed. And that the important major suit game propects are immediately clarified early on when playing against expert opponents (they can bid vigorously to put us in the dark if fit is not even confirmed). And that it is relatively rare to have good results to search just for the 4th suit as a possible fit when opponents has opened and responded while we are still bidding with unknown situation at the two level.