Nicholas,
It's a long time since I saw, and used, your little screwdriver, possibly 35 years or so. The secret is, if it's what I think it is, is that it opens up, I forget where, possibly the top, and holds another three blades of varying, smaller, sizes inside.
Used when I was a GPO/BT technician. Screwdriver, Watchmakers perhaps?
Regards,
Peter G. Shaw
Edited By Peter G. Shaw on 09/04/2014 19:57:10