The small HP knobs are 0.050" (50 thou). Get good quality ones or they will 
damage the screws.
I once found sone marked 1.27mm. The company found a random key that fitted a 
part they bought in, measured it in metric and ordered 50 custom keys in that 
size!

Robert G8RPI.

> On 16 November 2018 at 14:19 "Dr. David Kirkby" 
> <[email protected]> wrote:
>
>
> I have a few HP 5370B time-interval counters of various states of cosmetic
> and electrical condition. I wish to swap some knobs between the
> instruments, as some are in better condition than others. Can anyone tell
> me what size of hex key these are? I wish to order a hex key, but
> obviously, want one the correct size.
>
> Dave, G8WRB.
>
> --
> Dr David Kirkby Ph.D C.Eng MIET
> Kirkby Microwave Ltd
> Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD,
> Essex, CM3 6DT, United Kingdom.
> Registered in England and Wales as company number 08914892
> https://www.kirkbymicrowave.co.uk/
> Tel 01621-680100 / +44 1621-680100
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