BSF and Whitworth “Across the flats ” sizes.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 15/09/2020 17:08:31:

[…]

Clutch is my favourite – can't be undone!

Dave

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When my Dad worked at GKN, in the early 1960s … I remember these being colloquially known as ‘Jail Door Screws’

… Can any inmates confirm that usage ?

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Yes, Michael, that is how I knew them

They were fitted to the toilet door hinges in the, then new, Shrewsbury Technical College, in the 60s

More recently, my wife was a volunteer and fund raiser for an animal refuge, and one of the local lads decided to unscrew the lock to the washroom / store. purely vandalism since only animal food and dishes were kept there.

So, I milled some ordinary wood screw heads to a taper on one side and completely away on the other. The screws retained a plate which covered the lock, to prevent screwdrivers or levers being inserted to force the lock, and door open.

Break in attempts soon stopped!

They are quite effective

Howard

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Howard

It looks like we owe the original concept [since developed by others] to F. Salmen Jr.

**LINK**

https://worldwide.espacenet.com/patent/search/family/024137129/publication/US1956963A?q=US1956963

MichaelG.

[Author]

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