Patent applications must satisfy the following three criteria:
This means that your invention must not have been made public – not even by yourself – before the date of the application.
This means that your product or process must be an inventive solution. It cannot be a solution that would be obvious to a manufacturer. Take the example of a different attachment method. Instead of welding the tubes of a swing together, they might be screwed together. This may well be a new method of making swings. But for someone involved in making them, it is too obvious a solution to be called an inventive step.
This criterion implies that it must be possible to actually manufacture the new invention. In other words, you can apply for a patent on a new kind of playing card that is easier to hold than existing cards. But you can’t obtain a patent for an idea for a new card game.