Negative doubles after an overcall vary according to the suit opened and the suit overcalled.
After a minor-suit opening, negative doubles can be played thru four hearts, bringing spades into the picture.
SPECIAL DOUBLES
Negative thrufour heartsover a minor
_________________________________________________________________________________________________________
After a heart opening, negative doubles should be played thru three clubs, bringing diamonds and spades into the picture and staying below 3NT.
After a spade opening, negative doubles should be played thru three clubs, bringing diamonds and hearts into the picture and staying below 3NT.
After a major-suit opening, the thrump double has more value after anovercall of three diamond or after an overcall of three of the other major.
SPECIAL DOUBLES
Negative thru three clubs over a major
_________________________________________________________________________________________________________
1♥ (3♦/ 3♠ ) x=asking for stopper
1♠(3♦/ 3♥) x=asking for stopper
The thrump double: Do you want partner bidding the other major or four clubs when all you may need is a stopper in their suit?
Benefits include:
Plus... it's free!