Bridge:Conventions/1430 RKC Blackwood
After a fit is established, bidding 4NT asks the other player to tell how many key cards are held. Aces are key cards as is the King of trump. If no fit has been found, then the last suit named is presumed to be trump.
The responses are by steps.
Minor Suit Slams
If the agreed on suit is a minor, then 4 of that Minor is used as well. The responses are by steps, just as over 4NT.
This is very handy, because it saves space in the auction and allows a sign-off in five of the minor. The other nice result is that you rarely end up playing in four of a minor, and are strongly discouraged from bidding it.
Asking about Kings
After the response, bidding the trump suit at any level is a signoff. If the location of the trump queen is not known, then bidding the first available non-trump bid asks about the queen of trump. Bidding the next available non-trump bid asks for kings. If No Trump is not one of these steps, then bidding it is a sign off.
If the queen of rump is asked for, bidding trump denies the queen. Bidding a suit asserts that both the queen, and a king in the named suit are held. Bidding No Trump, asserts the queen, and no king of rank lower than trump is held.
After that, bidding a suit asks for responder to bid 7 if the named king is held.