Different partners prefer different versions of RKCB and I am trying to make sense of it all. This is my premise: the key card ‘asker’ usually is the one with the bigger hand or more particularly with the greater number of key cards though this is not always so. Nevertheless, the asker is more often than not interested in whether the responder has 1 or 2 key cards. If asker wants or needs 3 key cards, perhaps he should not be asking. This being the case, one has to cater for the situation where responder has only a single key card so as to be able to opt out of slam. Playing 1403 OR 0314, there is no difficulty opting out of slam if trumps are Ds, Hs or Ss as the key card response is less than or equal to game; but with Cs as trumps, playing 0314 doesn’t work as with only a single key card, the response of 5D is too high to avoid slam. Therefore clubs should be played as 1403. From this, one can see that playing 1403 is also satisfactory for all suits. The only contrary argument I can think of is that the asker more often wants to know in the main whether there are 0 or 1 key cards in partner’s hands. I have looked at this for some time and believe it is far more common to be searching for 1 or 2 (rather than 0 or 1) key cards when slam is being considered. I would be interested in other comments or arguments for one system or the other.