Would you believe that there is more to discuss here than was included in the last bridge tip?
1) An improvement in RKC Blackwood is, as mentioned already, that the response to the general King Ask (5NT) is to show your cheapest king rather than the number of kings. Often a grand slam depends on you holding a particular king (for example, if partner holds a 5+ card side suit missing only the king). Now- if your response shows a king that partner doesn't care about, or if he needs to know about another king, he asks if you have that king by bidding 6 of that suit (providing it is lower in rank than the trump suit). If you have it, bid the grand slam.
2) The above principle is extended to the Queen ask. If your initial response to the 4NT bid was 5C or 5D, partner may not know if you also have the trump queen. He asks for this information by making the cheapest suit bid other than the trump suit. If you do not have it, sign off as cheaply as possible in the agreed trump suit. If you have the queen, cue bid your cheapest king. This gives partner 2 pieces of important information with one bid. If partner now needs to know about another specific king in order to bid a grand slam, he bids that suit. If you have this king, bid the grand. Otherwise sign off at 6.
3) If your initial response to 4NT was 5C or 5D, you are showing an ambiguous number of key cards. If partner needs you to have the higher number, he will sign-off at the 5 level and hope you are not already too high. If you have the higher number of key cards (3 rather than 0, for instance), you must bid on. Rather than just bidding the small slam, however, you should cue bid your cheapest king if you also hold the trump queen. This may enable partner to bid a grand slam. Without the trump queen, just sign-off at 6 of the agreed trump suit (denying the queen).
4) If you have a void in a suit that will not be a duplication of partner’s values (a useful void), you may show this in your response in several ways. This is the best (trust me).
