[straube]

We're using Adam and Sieong's NT structure with slight tweaking but at the point of

1N-2S, 2N/3C-3D responder is showing a 5D/5C hand and we don't know how to continue that.

I'm guessing

3H-antisplinter
.....3S-spade shortness
3S-antisplinter (doesn't like heart shortness)
3N-suggests a contract

Sound right?

And after such a start as 1N-2H, 2S-3D, 3H-3S we've learned that we have a 5-3 spade fit and that responder also has 5 diamonds.

Antisplinters there, too?

What should the bids of 3N, 4C, 4D, and 4H mean?

[awm]

For better or worse, we do not generally play "anti-splinters" except when a specific shortness has been shown. These calls are just cuebids/location of values for us. The auction to 3♠ seems like one where non-serious 3NT would apply.

[straube]

Thanks. That helps a lot. Wondering if after responder shows 5m/5m and opener shows strength in a major with 3H or 3S you can still play 3N. Thinking yes but maybe 3M implies interest in the minor.

Any rule of thumb for what meets the threshold of "no wastage"? My first thought was roughly 14 working points but maybe that's too stringent. 13? I'm assuming some 4432 hand with an 8-cd fit. Nothing special.

[Kungsgeten]

I don't know if opener has more information here, but I think its common after the "popular" 1NT-3D (showing GF and 5-5 minors) to play:

1NT-3D;
3H = Asks shortness.
3S = Not sure. Maybe could be used as a super-fit? Something like both major aces and a top honour in both minors?
3NT = Suggestion to play.
4m = Support, doesn't want to play 3NT.