The most common and most likely answer to this crossword clue is the 6 letter word COBBER
C
O
B
B
E
R
Buddy explains!

The straight part
We know that "china (plate – mate)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case china (plate – mate) = cobber.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does COBBER mean?
COBBER noun- A pal, buddy, mate, friend; often used in direct address by one male to another.
- A sweet consisting of a small block of hard caramel covered in chocolate.