Doubles. Double, then bid a suit
After you double enemy's opening bid, your partner will assume you have an opening hand, 12+ HCP, with a 4441 distribution.....
Strong hand, 16+
With 16+ HCP, rather than jump, simply "double" and then bid the 6-card suit on your rebid. With only a 5-card suit you'd need 18+HCP.
Pending your rebid, your partner will regard your double as a double for takeout, which is a forcing bid asking for his best suit. However, when you then switch suit, he'll realise that in fact you have 16-19 HCP and a long suit, and will readjust his thinking.
Super Strong
With 20+, in the old days, you would cue bid the opponent's suit. This is simply a point count, and a forcing bid and says nothing about your shape of suit preferences. Your partner should simply close his eyes and bid 2NT, so that you can then say what you really meant.
However, since this is such a rare situation, most players now use this cue bid as a Michael's cue bid, announcing one or two 5-card Major suits, which is not only much more common, but is also tremendously powerful.
If you do really have a powerful hand, more than 18 HCP with a 5-card suit, or 16 points and a 6-card suit, then you can first bid a forcing "double for takeout", and then, on the rebid you (the overcalling doubler) can go on to change suit, ignoring the one your partner has been forced to offer you. Partner should spot that something funny is clearly going on, which has a special meaning.
Similarly, a 2NT overcall used to mean a balanced hand with 20-22 HCP, but again it's such a rare occurrence that this unusual 2NT bid is nowadays employed to announce one or two 5-card minors, which again is both more common and much more useful.
Now try the quiz
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