Is it from a rack bolt?
One of these:
If so what you are looking for is a rack bolt keep plate. I can't find anywhere that sells them separately to the lock but Toolstation sells rack bolt kits in a pack of 2 for > £6 inc. VAT.
Not one of these but similar ta, bottom locks on double door mechanisms.
@rhb started
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Is it from a rack bolt?
One of these:
If so what you are looking for is a rack bolt keep plate. I can't find anywhere that sells them separately to the lock but Toolstation sells rack bolt kits in a pack of 2 for > £6 inc. VAT.