Redesigned seat fitted with wide strap (5)
I believe the answer is:
tawse
'strap' is the definition.
(tawse is a kind of strap)
'redesigned seat fitted with wide' is the wordplay.
'redesigned' indicates an anagram.
'fitted with' means one lot of letters goes inside another.
'wide' becomes 'w' (abbreviation e.g. in cricket).
'seat' is an anagram of 'tase'.
'tase' going around 'w' is 'TAWSE'.
(Other definitions for tawse that I've seen before include "Strap once used for punishing schoolchildren in Scotland" , "Thong for punishment" , "Retribution for Scots" , "Leather strap once used to punish Scottish schoolchildren" , "Used for corporal punishment" .)