This is an example from my Jacoby Two No Trump workshop of standard cuebidding to find slam.
The bidding: South opens One Spade and North shows an opening hand with four-card support. South has a second five-card suit, but it is not good enough to bid Four Diamonds. KQJxx is good enough not KQxxx. Instead, he shows his singleton or void in Hearts.
Like a splinter, it cannot be a singleton Ace, King or Queen because partner will incorrectly discredit any King or Queen he has in the suit.
Because North has Axxx (or xxxx) opposite partner’s singleton, slam makes on 27 HCP’s which he knows they have. He bids 3 showing slam interest and asking partner to cuebid his first round controls. South has none and bids Four Spades.
North then bids his first round Club control, and South can now show second round control in Diamonds. That is what North needs to hear so he bids Six Spades.
North could not use keycard Blackwood because of his worthless Diamond doubleton. One does not ask for Aces when one needs to know which Ace not the number of Aces.
When playing standard cuebidding, not the Italian style, a cuebidding sequence is started once a suit has been determined and a game force is on. New suits are cuebids showing controls. One can no longer find secondary fits once Jacoby 2NT has been used and South did not bid a suit at the four-level.
When a player bids a side suit at his first chance to bid that suit, he shows first- round control (Ace or void) and denies first round control in any suit he skipped.
When a player bids a side suit at his second chance to bid that suit or when partner has already shown first round control, he is showing second-round control (King or singleton). He denies second-round control in any suit he skipped.
The Play: West leads a trump. South draws trump, loses the Diamond Ace, ruffs a Diamond and pitches a Diamond on a Club to make his slam for +980.