Latch, square on the narrow part (5)

I believe the answer is:

sneck

'latch' is the definition.
(I know that latch can be written as sneck)

'square on the narrow part' is the wordplay.
'square' becomes 's' (abbreviation).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'the narrow part' becomes 'neck' (I've seen this in another clue).
's'+'neck'='SNECK'

I've seen this clue in the Sydney Morning Herald.

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