[johnu]

I am only familiar with the name Spiral Raises for using 2NT (2♠ after a raise in hearts) to check on trump length, hand strength, and distribution depending on the version you are using.

[fromageGB]

 Vampyr, on 2016-April-20, 06:38, said:

I am not sure how common it is but it seems intriguing.

Place four North-American textbooks round a table and observe carefully. More common than you think.

I play the 5656 2NT convention in response to a weak 2M open : weak 5, weak 6, strong 5, strong 6.

[kenberg]

 johnu, on 2016-April-20, 12:01, said:

I am only familiar with the name Spiral Raises for using 2NT (2♠ after a raise in hearts) to check on trump length, hand strength, and distribution depending on the version you are using.

You are ahead of me. Gavin Wolpert has something on spiral for 1m-1M-2M, where 2M is possibly on 3, on BW
http://bridgewinners.../spiral-raises/

He remarks that it can apply after 1♥-1♠-2♠ as well, such as here. I am willing to believe it has merit (or at least I am not up for debating the issue with Wolpert). I like his observation that it has been useful for getting out in 3NT on a 4-4 fit when both players have weak trumps. It is true that in the natural approach I use we seldom, I won't say never, end in 4M on a 4-3 fit unless we want to, but we have no real way of finding 3NT in the weak 4-4 case.

[Zelandakh]

Variations on the 3344 convention have come up many times on BBF, for example here, here, and here. I am fairly sure all of the BBF regulars have seen the convention at some point!

[lycier]

So this question is simple, its convention is simple
Doesn't need more discussions

[ahydra]

 lycier, on 2016-April-21, 07:02, said:

So this question is simple, its convention is simple
Doesn't need more discussions

Something doesn't make sense about the way you described it though. Surely with a 21-count opener is not just going to raise to 2M, lest responder pass and you miss the coldest 3NT/4M ever missed. In practice I suspect the range of 2M would be more like 11-16, with opener preferring a natural reverse or some other bid with more than that. And to be honest even making that bid with 16 HCP might risk missing game (since with a borderline invite, responder will think "he's far more likely to have 11 than 16").

ahydra

[Zelandakh]

Yes, lycier wrote "maximum opening hand" rather than "maximum simple raise". In practise the range is likely to be ~12-15 or so TP.