What is the principle of blocking the means (Sadd al-Dhara'iʿ), and what are examples of Imam Malik's application of it?

"Sadd al-Dhara'i'" (blocking the means) is a fundamental principle in the Maliki school, and its meaning in both language and Shari'a is quite similar. Linguistically, it refers to the means that lead to something. The scholars of the Maliki school have emphasized the validity of this principle, considering it a sign of the Imam's meticulousness and piety. His madhhab is built upon blocking the means and avoiding doubtful matters. Among its applications are: the prohibition of using vessels made of gold or silver, the obligation to block the means (to evil), treating suspected riba (usury) as equivalent to confirmed riba, the prohibition of selling grapes to someone who will press them into wine, and the prohibition of selling weapons to someone who intends to commit highway robbery or incite sedition.