Where can I get one of these . . . . . . . ?

[TheSalad]

Where can I get one of these please. It's the little cylindrical screw that goes in to the door handle mechanism, unscrewed using an allen key. This one appears to have fallen off and probably been hoovered up.

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Also, could someone tell me what sort of screwdriver fits these please?
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Many thanks.

 

[TheSalad]

Here is a better image of the (grub?) screw I'm after, taken from one of the other doors?

View media item 89421 View media item 89422

 

[Burnerman]

It is an Allen grub screw you need, plenty on ebay and amazon etc......unfortunately we don't know which thread it is......it looks a bit coarse to be metric, could be BSW.
The other one is a posidriv, number 2 size by the looks of it.
John