It has an engraved monogram - possibly "JC" or "CC" and a baron's crown.
Such cases are sometimes known as "roundlets", possibly because they are small and round (at least in one direction), or possibly referring to an old term for a small barrel.
They could contain gadgets such as picnic cork screws, or, as in this case , carriage keys.
The case unscrews to reveal a square section key. This can be pulled out and rotated to lock into position and the case/ handle screwed back together.
