This is a Uilleann Chanter Connector, it is made of Indian ebony. It has a brass fitting which has a connecting curved brass tube with thread on the end.
You connect the chanter, with its reed in place, to the ebony chanter stock. Slide the curved brass tube of the ebony chanter stock into the small hole in the wooden chanter connector on the Bag's neck.
Opening is 5/8 inch in diameter.