Borosilicate glass window suitable for mounting multiple glass tritium vials (tritium vials not included). (3) bores equally spaced around center spindle shaft. Each bore can hold (1) 3mm x 23mm vial. 0.472'' outside diameter. Comes with (5) glass window O-rings, (2) spindle groove O-rings, (2) glass windows, and (1) split rings for attachment. Bulk packed.