While many Dutch words just take -je to form a diminutive, others require -kje, -etje, -pje, or -tje depending on their final sounds.
The Suffix -kje
When a noun with more than one syllable ends in an unstressed -ing (like ketting), drop the final g and add -kje.
The Suffix -etje
The ending -etje is used for short, one-syllable nouns ending in -ng. Unlike longer words, the g is not dropped.
You also use -etje when a word ends in a single consonant following a short vowel. To keep the short vowel sound intact, double the final consonant before adding the suffix.
The Suffix -pje
When a noun ends in -m preceded by a long vowel, a diphthong, or another consonant, add -pje to create the diminutive.
Note: There are a few common exceptions. For example, some nouns ending in *-m, like bloem (flower), take -etje instead of -pje.*
The Suffix -tje
Nouns that end in a vowel, or in -l, -n, -r, or -w preceded by a long vowel or an unstressed syllable, usually take -tje (such as tafel becoming tafeltje).