101 × 8 × 8 mm

This mystery object is 10 cm long when closed up and was given to me by an antiques dealer who had a yellow  cloth roll holding about 20 of them, apparently all identical.

At one end is a roughly ground point, with a small flat at the end. At the other end is a thin extension with a sort of chuck at the end which captures the two free ends of  a loop of nylon(?) bound with thread. .

There was a spare loop inside the tube.

What is it?