Here's a breakdown:
* Single Consonant: The final consonant must be a single letter, not a consonant blend (like "sh" or "th").
* Preceded by a Single Vowel: The consonant must be directly before a single vowel.
* Stressed on the Last Syllable: The emphasis of the word should be on the final syllable.
Examples:
* Doubled:
* hop (hopping)
* beg (begging)
* run (running)
* Not doubled:
* cook (cooking) - The stress is on the first syllable.
* train (training) - The final consonant is followed by a consonant blend.
* play (playing) - The final consonant is followed by two vowels.
Remember, there are some exceptions to this rule, but this provides a good starting point for understanding when to double the final consonant.