In standard four-ace Blackwood, following the 4NT ask and and the ace-count response, a bid of 5NT asks partner about his king holding.
In other versions of these conventions a bid will be designated with this same meaning.
Many pairs play that the next suit up other than the agreed trump suit will carry this message. Take particular care with this approach if playing Roman key-card Blackwood. You will need to ensure that your king-ask does not clash with your search for the trump queen.
Other pairs will play that 4NT asks for kings if this bid is still available. Clearly this will only apply if playing something like Kickback or Redwood, but you might regret not being able to finish in a natural 4NT once a minor suit has been agree.
Come to your own partnership agreement, but the simplest and safest agreement is that the king ask will be in the same denomination as the original asking bid. Thus if 4♥ was your key-card ask with diamonds agreed then 5♥ will be your king ask.
Use with care
Many beginners will follow their simple Blackwood 4NT with 5NT asking for a count of kings, almost without thinking.
I cannot emphasise too strongly that this is usually the wrong action.
I will not be telling you anything new when I remind you that asking with 5NT already commits you to a small slam and so there is no point in making this bid unless you have an interest in a grand slam. With this in mind, you will not make such a bid unless your side holds all the key-cards and the queen of any prospective trump suit. Very occasionally partner will use this information to bid the grand himself rather than to give you a count of kings as requested.
If you want to be in a small slam but you have no interest in a grand slam then just bid it.
But just in case a grand slam is a realistic possibility, here are two possible versions of the convention.
The first is that usually taught at an early stage.
Giving a count of kings
In the standard method the count is exactly the same as for aces, only a level higher.
6♣ 0 or 4
Some will bid 6NT with all four kings.
Note that if playing a key-card ask rather than an ace-ask then you will confine your answer to ‘the other three kings’.
Beginner and above
Post intermediate and above
A better alternative is to respond with information about the specific kings held, rather than a potentially ambiguous number.
The specific king ask
In the following I shall refer to the bid of 5NT following your RKCB 4NT enquiry. The methods adopted are easily extended to the equivalent bids following a kickback, redwood or minorwood enquiry.
Locating the right king is frequently as important as locating the right ace. A simple solution is to respond to the 5NT king ask by bidding the specific king held rather than the number of kings held. As discussed above, you can only make such an enquiry if you are interested in the possibility of finishing in a grand slam and so you must already hold all the key-cards.
There are a number of ways of implementing the responses to this end.
Simplest is to use a bid in the agreed suit to show no side-suit kings, a bid in any other suit to show precisely one king in that suit, and with two kings you should jump directly to the grand.
As with all of these conventions it must be used with care, but it is a distinct improvement on the simple set of quantitative responses.
It is just about possible for partner to hold zero key-cards for this sequence.
If this is your reading of the situation then sign off in 5♠. Partner will raise to 6♠ with three. If you’re a gambler you can then try seven, but it could easily depend on the heart finesse - not usually a good choice.
Alternatively, assume that partner holds all three key-cards - more than likely.
If so, bid 5NT - the ‘specific king ask’.
If partner signs off in 6♠ showing neither red suit king then pass. You will be able to throw the second diamond on the ♣A, and you may or may not lose a heart;
if partner bids 6♦ promising the ♦K but denying the ♥K you will again sign off in 6♠, and the overtrick will depend on the heart finesse;
if partner bids 6♥ promising the ♥K but denying the ♦K then I would bid 7♠, expecting to throw any diamond losers on a long heart;
And if partner bids 7♠ with both kings then you can just about count fourteen tricks - either pass or convert to 7NT in pairs.
A good convention - preferable to 5NT asking for a count of kings,
but whichever of these you have agreed use it sparingly - it will frequently not be the right bid.
A Q J 8 4
A Q J 6 3
2NT is Jacoby, agreeing spades and forcing to game.
Your 3♣ shows shortage, and 3♦ by partner promises a first or second round control.
4NT is RKCB and 5♣ shows 0 or 3.
This page last revised 18th Sept 2018
Context -The continuing auction - in the slam zone - Blackwood etc..