Grand having American firm providing joint support (6)
I believe the answer is:
gusset
'joint support' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'grand having american firm' is the wordplay.
'grand' becomes 'g' (G is short for grand as in a thousand).
'having' is a charade indicator (letters next to each other).
'american' becomes 'us' (abbreviation for United States).
'firm' becomes 'set' (both can mean fixed).
'g'+'us'+'set'='GUSSET'
'providing' is the link.
Can you help me to learn more?
(Other definitions for gusset that I've seen before include "Strengthening piece of material" , "Inset piece of fabric" , "Strengthening insert in garment" , "Piece inserted to strengthen or enlarge a garment" , "Piece inserted into garment for enlargement" .)