Abstract: An insert for providing a seal at the junction of axially aligned bores extending through two adjacent segments of material. The insert is of a rigid material, has an inner diameter equal to the diameter of the bore, and comprises a retaining portion with a frusto-conical outer surface and a stem portion with a cylindrical outer surface. The insert is retained in a co-axial recess which extends inwardly from the face of one of the segments of material. In this manner, the retaining portion of the insert and the walls of the recess define a groove for retaining an O-ring. Also described is a method of providing a seal at the junction of axially aligned bores extending through two segments of material. The method includes the steps of boring a recess in one of the bores, introducing the insert into the recess, retainably inserting an O-ring into an annular groove defined between the insert and the recess, and bringing the segments together.