Makes more flat golfing equipment (5)
I believe the answer is:
irons
This clue is a double definition.
'makes more flat' is the first definition.
(to iron clothing is to make it flat)
'golfing equipment' is the second definition.
(iron is a type of golf club)
(Other definitions for irons that I've seen before include "instruments of restraint" , "Devices restricting personal freedom in prisons" , "Don't have too many in the fire, we're told" , "Golf-clubs with metal heads" , "English player" .)