In message , Jim GM4DHJ ...
writes
On 06/05/2020 08:03, Graeme wrote:
My Google-fu is having a day off.* Any idea what that type of binder
was called?

Crown binder? ...

Certainly looks similar. The paper, though, had two cut outs down one
long edge, each T shaped like this :

!
!
! ___
! ! !
----! !
! paper formed around strap
----! !
! ! !
! ---
!

I have six crank keys here, four brass and two plated. I'm sure the
plated ones were for the binder.
--
Graeme