Source: ABF Bulletins 
Bidding grand slams is a matter of confidence, as well as system. Some players bid too many, some too few, and some bid none at all. But if you bid and make a grand slam, you will normally win a swag of IMPs or matchpoints. Most slams are bid through Key Card Blackwood. 5NT following the response to Key Card Blackwood guarantees that the partnership holds all fi ve Key Cards plus the trump queen. This is your key to bidding more grand slams.
First and foremost, 5NT is an invitation to bid seven. The message is “Count our tricks partner, and bid seven if you can.” If the total comes to less than 13, then the Key Card responder shows specific kings. Most times, the number of kings is irrelevant, it is the precise king or kings that the Key Card asker wants to know about.
1. 20-22 balanced.
2. Transfer to 3.
3. Natural, second suit,.
4. 2 Key Cards, and the trump queen.
How should opener continue on these hands:
1. 6. First thing is whether you should bid 7 right away. Count your tricks, knowing the partnership holds all the Key Cards plus the trump queen. You have five spades tricks, two hearts, two diamonds, and one club, only 10 tricks. Respond 6 to show you have K. If partner needs you to have K then partner will continue with 6 over 6. This says “bid 7 if you have K.”
2. 6. Again, you can’t count 13 tricks, so you dutifully show which king you have.
3. 7. In 7, you can count five spades tricks, two hearts, three diamonds and two clubs – and one club ruff in your hand. Knowing your partnership has all the Key Cards + trump queen, you have 13 tricks in spades unless trumps break 4-0.
4. 7NT. An important part of slam bidding is whether to play in notrumps, or stay in the security of a suit contract. In notrumps you can count 13 tricks – five spades, three hearts, two diamonds, and three clubs. Responder held 107643, A, A, AJ10652. 7 is in danger of failing on a 4-1 trump break, or a club ruff at trick one. 7NT has 13 top tricks, without the spade break, and without the risk of an adverse club ruff at trick one.
Sometimes you need a specific second or third round control:
1. Cuebid agreeing hearts.
2. Cue, first or second round control.
3. Key Cards.
4. Direct Ask.
5. K and not Q.
K was the vital card on this deal. 5 simply said “What do you have in spades?” The responder had already cuebid a diamond control, so the second round of spades is the only problem. Ron Klinger recommends the following responses to the Direct Ask:
1st Step No Queen, no King
2nd Step Queen, not the King
3rd Step King, not the Queen
4th Step King + Queen
Sometimes the Key Card responder can’t count thirteen tricks, but has substantial extras, and can judge there will be good chances for 13 tricks:
This is an easy 7 bid. Three trumps to the jack is a plus, and AKQ means lots of extra tricks. There is little point in bidding 6, as you will be past 6. The expert bid is 7, knowing that there are probably 12 top tricks, and numerous chances for the 13th.