On Mon, 16 Mar 2015 14:16:52 +0000, DerbyBorn wrote:

I have never seen one with a slotted screw. Are you sure it isn't a
broken off shaft that lookes like a screw slot?

Most "lockshield" valves are ordinary valves but with a cap rather than
a knob.


You should get out more!
My c1975 c/h is fitted with them:

https://www.dropbox.com/s/t1iwumq5z4...hield.jpg?dl=0

--
TOJ.