[maris oren]

Opponents-1 ♠. Partner X (ti double). Opponent passes. I have to respond to my partners X/

What happens if opponent overcalls after my partners X. what are the rules for responding to my partners . Do I need a certain no. of points?

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[Cyberyeti]

Rules vary, this is a good place to play Lebensohl or one of the variants of it so you can use 2N as an artificial bid with partner bidding 3♣ unless really strong, giving you two ways of getting to say 3♥ one of which is better than the other.

[mycroft]

In addition to Cyberyeti's answer - which I thoroughly endorse, with the caveat of "only if you're really really comfortable with Lebensohl thinking"; treating 1♠-X-2♠ the same as 2♠-X-p makes a whole lot of sense in context - you should know with partner how aggressive you bid against 2-of-a-fit auctions.

There's 40 points in the deck, no more, no less; in non-strong games, the opponents have shown 17 or so of them (in stronger games, the opponents have shown 12 or so of them, especially if they play transfers after 1M-X); partner should trust that you're not "a big hand" when you call anyway (which is why Lebensohl - the rare times you do have the big hand you need a way to show it!) Partner should not hang you for bidding shape; if they do, time for another discussion on "how aggressive you bid against 2-of-a-fit auctions". At least one of you has to change.

Note: there is no "right answer" to this question. It's a matter of partnership taste. I happen to believe so strongly in "very" being the right answer that the opponents are shocked and scared when we let them play 2M fit (at least the good players are; and they should be). Backing off a fair bit, especially at IMPs or just to be comfortable, is fine; but it means that here you do "promise some strength" when you bid, and will miss some nice competitive auctions (and partner will have to balancing double more aggressively, which can lead to the same problem you were trying to avoid by "promising some strength").

The key is, like a lot of things in bridge, it matters less where you and partner are on that spectrum, than that you and partner agree on where you both are. And you don't have to be in the same place with every partner (I'm certainly less "balance in direct seat" with a newer player that I haven't played much with or against, for instance, than I am with my regular partners).

TL;DR: ask partner. Get an answer you're willing to live with. Bid that agreement. Discuss if that agreement should change if you're getting too many poor results - but "Bid that agreement" until *after* that discussion.