It is the base for the screw driver bit in one of the tubes. You would insert the screw driver bit into it and tighten the set screw on the bottom. Then you use it to secure one end of the strap/bracelet pins while using the supplied screw driver on the other.
It's a wotsit. In one of the glass tubes there is a little screwdriver blade for removing the strap/bracelet. By inserting it into the base that you are holding in the pics you can then tighten the grub screw on the base using the other driver and you have 2 totally gimmick free screwdrivers.
The jeweler screwdriver is O.K. but I tend to use the little stubby thing like a normal driver as I feel that I have more control over it.
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