Iron bolt secures West End joint (7)
I believe the answer is:
fetlock
'joint' is the definition.
(fetlock is a kind of joint)
'iron bolt secures west end' is the wordplay.
'iron' becomes 'fe' ('Fe' can be a synonym of 'iron').
'bolt' becomes 'lock' (I've seen this before**).
'secures' indicates putting letters inside.
'end' says to take the final letters.
The final letter of 'west' is 't'.
'fe'+'lock'='felock'
'felock' going around 't' is 'FETLOCK'.
(Other definitions for fetlock that I've seen before include "Projection above a horse's hoof" , "Equine leg joint" , "beastly joint" , "Hair above horse's hoof" , "Horse's leg joint" .)