This is a convention you use to ask for aces with 4NT. What makes this convention different from the old BlackWood? The king of trump is used as the fifth ace. And you can ask for the queen of trump. This is how you bid RKCB:4NT- 5C : 0-3 Aces 5D : 1-4 Aces 5H : 2 Aces without the queen of trump. 5S : 2 Aces + the queen of trump.If partner bids 5 club or 5 diamond you can ask for the queen of trump in the nearest suit thatisn't the trump suit. This is how you replay: Lowest possible in the trump suit: Denies the queen of trump.With the queen of trump, you answer: lowest not shown cuebid, or 5NT without new cue.Remember that you don't have to have all aces to ask for the queen of trump. So you can't jump to 7 just because you have extra length in the trump suit.When you partner has answered his aces or the queen of trump you could bid 5NT. The responder shows lowest not shown cuebid. 5NT promise all aces, but you are not sure about the rest. 5NT is a invitation to grand slam. If the responder on 5NT has a lot of extra strength (or length) he bids 7 directly. If you are in doubt just bid the suit you have extra strength. Start as low as possible. This could be a king you haven't shown or KQ combinations in a suit you have promised control in. The 5NT may also show extra strength in a suit if he still isn't sure about the grand slam.Another tips is to reverse the two first steps on 4NT - called 1430 RKCB. Why? Because 1 ace is more frequently then 0 aces, and you save some space! If heart is trump you won't get the chance to ask for the queen under the 5 heart:4NT - 5 Diamond (1-4 aces)Now you have to use 5 spade to ask for the queen of trump, and then you are in 6 anyway, but:4NT - 5 Club (1-4 aces) Now you can ask with 5 diamond and pass on 5 heart!!