NT Transfer to ClubsTwo means are available for showing 6+ card minor suits in response to a 1N opening bid. One method is to jump directly to 3. Another way is to use 2 as a transfer to 3.
2 is available to use as a transfer bid because virtually everyone plays Jacoby transfers, so that with a Spade suit, they bid 2, asking partner to bid 2, rather than bidding 2 themselves.
The problem is that while there are two methods for showing long Diamonds, there are at least 3 different possible hands with long Diamonds: weak (sign-off), invitational, and strong (slam interest).
(In addition, within each of these hand strengths, you can have weak, good, or solid Club suits, but showing each of these is beyond the scope of this convention.)
Bidding The Minors In SAYC
Standard American Yellow Card ("SAYC") only provides for two types of hands, weak and invitational.
The weak hand is shown bidding 2 as a transfer to 3, then either passing 3 or correcting to 3 if that is the long minor suit held.
The invitational minor suit hand is show by jumping to 3 or 3 directly.
In SAYC, the minor-suit hand with slam interest can be shown by making a quantitative 4N raise over 1N or by bidding Gerber to ask for Aces.
For the casual partnerships for which SAYC is intended, the above methods should be sufficient, since slam-oriented hands which cannot be handled by the above come about very rarely.
Showing Slam Interest
An additional bid for showing slam interest can also be used which is not part of SAYC as such, but which even casual partners should be able to reason out at the table:
With a strong hand, first bid 2 to transfer to 3 as you would with a weak hand, but then bid either 4 or 4 over 3 to show a slam invitational hand with a good 6+ card Club or Diamond suit. If opener does not wish to go to slam, he can sign off at 4N.
Signing off with 4N precludes being able to bid 4N for Blackwood, and casual partnerships should just accept that rather than trying to remember more complications for a situation which is extremely unlikely to arise.
Regular partners should agree to use the next higher suit over 4 as asking for Aces (or preferably, for key cards). This is, in fact, highly preferable to bidding 4N for aces/keys because you can still get out at either 5 of the minor, if necessary. (Although at matchpoints, if slam isn't on, you will want to be in the higher-scoring 5N rather than 5.)
Over 4 use 4 and over 4 use 4 to bid Blackwood (or RKCB for the minor suit), and leave 4N as the sign-off. This has the advantage of starting Blackwood at a lower level. In response to 4 (assuming RKCB), 4 shows 1 or 4 key cards, 4N shows 0 or 3, 5 shows 2, and 5 shows 2 keys with the Queen of Diamonds (trumps). The replies to 4 (over 4) are the same, but one suit lower, starting with 4 to show 1 or 4, etc.