Abstract: A device (10) adapted to position a ring (R) in the bore (B) of a cylinder (C) so that the ring (R) is perpendicular to the axis of the cylinder (C) includes a first segment (11) and a second segment (12). The first segment (11) has a tongue (20) which is slidably received in a groove (34) in the second segment (12). A threaded shaft (37) of a hand screw (35) is received through the groove (34) and into a threaded aperture (21) in the tongue (20) to attach the first segment (11) to the second segment (12). Arcuate surfaces (18) and (27) of the first and second segments (11, 12), respectively, define a portion of the circumference of a circle approximately the diameter of the bore (B) when the segments (11, 12) are attached to each other. The ring (R) is positioned in the bore (B) and the device (10) is inserted in the bore (B) until the lip (19, 28) of the first and second segments (11, 12) rest on the top edge of the cylinder (C).