Are there other explanations of ”right hand” than masturbation (Matthew 5:30)?

Let's look at the narrow context:

Adultery

27 “You have heard that it was said, ‘You shall not commit adultery.’ 28 But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart. 29 If your right eye causes you to stumble, gouge it out and throw it away. It is better for you to lose one part of your body than for your whole body to be thrown into hell. 30 And if your right hand causes you to stumble, cut it off and throw it away. It is better for you to lose one part of your body than for your whole body to go into hell.

Matthew 5:28 obviously states that an adulterous thought or look is a sin in itself.

Now, an act is of greater significance than thought. Masturbation is an act in line with adulterous thought, furthermore, it implies it most of the time.

I don't know if 'the right hand' had an implication in Hebrew as it does in Croatian (I don't even know if it has a sexual implication in English), so I won't take that as an implication forbidding masturbation.

The whole passage is also a very cautious one. It encourages you to take measures to prevent yourself from sinning. In light of that, we can also conclude you shouldn't mast**bate, at least as a precaution since you are having doubts if it is sinful.

If you aren't just interested in Matthew 5, Genesis 38:8-10 clearly implies sexual acts against nature (not leading to procreation), such as masturbation and contraception are sinful.

However, that is just my opinion, so I'll leave you with something of actual worth. The Catholic Church's binding teaching (not defined here, but condensed in the CCC):

CCC 2352 By masturbation is to be understood the deliberate stimulation of the genital organs in order to derive sexual pleasure. "Both the Magisterium of the Church, in the course of a constant tradition, and the moral sense of the faithful have been in no doubt and have firmly maintained that masturbation is an intrinsically and gravely disordered action." "The deliberate use of the sexual faculty, for whatever reason, outside of marriage is essentially contrary to its purpose." For here sexual pleasure is sought outside of "the sexual relationship which is demanded by the moral order and in which the total meaning of mutual self-giving and human procreation in the context of true love is achieved."

Here is also the passage on contraception:

2370 Periodic continence, that is, the methods of birth regulation based on self-observation and the use of infertile periods, is in conformity with the objective criteria of morality.158 These methods respect the bodies of the spouses, encourage tenderness between them, and favor the education of an authentic freedom. In contrast, "every action which, whether in anticipation of the conjugal act, or in its accomplishment, or in the development of its natural consequences, proposes, whether as an end or as a means, to render procreation impossible" is intrinsically evil:

> Thus the innate language that expresses the total reciprocal self-giving of husband and wife is overlaid, through contraception, by an objectively contradictory language, namely, that of not giving oneself totally to the other. This leads not only to a positive refusal to be open to life but also to a falsification of the inner truth of conjugal love, which is called upon to give itself in personal totality. . . . The difference, both anthropological and moral, between contraception and recourse to the rhythm of the cycle . . . involves in the final analysis two irreconcilable concepts of the human person and of human sexuality.

I encourage you to read the context in the Catechism.

Among the commandment of the Law is against adultery. Jesus says that you heard that it was said: you must not commit adultery, for he was quoting from the law. He continues, but I say to you that everyone who keeps on looking at a woman so as to have a passion for her has already committed adultery with her in his heart. (Matthew 5:27, 28). We read that Jesus is not speaking merely about a passing sexual immoral thought, but rather, he is also stressing the seriousness of the matter when one keeps on looking and what follows concerning that. Continued looking often arouses passionate desire, and it promotes the taking of action, hence masturbation. If an opportunity arises, it can result in adultery, as is with sexual immorality. But this can be prevented for a person evade such a thing and prevent anything else from happening. We continue on with Jesus words, if, now, your right eye is making you stumble, tear it out and throw it away from you. . . . If your right hand is making you stumble, cut it off and throw it away from you (Matthew 5:29, 30).

Jesus says that it is more important to throw away anything away, even something as precious as an eye or a hand (most certainly not literally), to avoid immoral thinking and its resulting actions. For it is better for you to lose one of your members [body members/body parts], Jesus explains, than for your whole body to land in Gehenna [Hinnom and or place of total destruction]. Gehenna derives from an area outside Jerusalem’s walls to get rid of trash and or rubbish, The Valley of Hinnom).

All and all, do not be bested by sexual immorality, should you or anyone else fall, remember, you can always get back up to fight against it, Proverbs 24:16.