Half of metal for a mug’s seat (3)
I believe the answer is:
pew
'mug's seat' is the definition.
'pew' can be an answer for 'seat' (pew is a kind of seat). I'm not certain of the 'mug's' bit.
'half of metal' is the wordplay.
'half of' indicates taking half.
'metal' becomes 'pewter' (pewter is a kind of metal).
'pewter' with half the letters taken is 'PEW'.
'for a' acts as a link.
Can you help me to learn more?
(Other definitions for pew that I've seen before include "Where some of the flock rest" , "Bench-like seat in a church" , "Long bench in a church" , "Long church seat" , "Part of flock sitting here" .)