Fasten right in line (4)
I believe the answer is:
tier
'line' is the definition.
(tier is a kind of line)
'fasten right' is the wordplay.
'fasten' becomes 'tie' (tying is a kind of fastening).
'right' becomes 'r' (common abbreviation).
'tie'+'r'='TIER'
'in' acts as a link.
(Other definitions for tier that I've seen before include "one doing Bond" , "He might do sailor's knots" , "Row, level" , "Echelon" , "One making knot - level" .)