Two posh male guards deliver something metallic (7)
I believe the answer is:
iridium
'something metallic' is the definition.
(iridium is a metal)
'two posh male guards deliver' is the wordplay.
'two' becomes 'ii' (roman numeral).
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-u).
'male' becomes 'm' (common abbreviation).
'guards' means one lot of letters goes inside another.
'deliver' becomes 'rid' (I've seen this in other clues).
'ii'+'u'+'m'='iium'
'iium' going around 'rid' is 'IRIDIUM'.
(Other definitions for iridium that I've seen before include "Corrosion-resistant metal, Ir" , "Heavy brittle metal used in alloys, Ir" , "Metallic element resistant to corrosion, atomic no. 77" , "Colourful compounds come from this" , "Silvery-white metal" .)