A Mons trans is a metal holder
A Mons trans (also called Ostensorium) is a part of the liturgical crockery in a (Catholic) church. The holder (usually of metal) has a consecrated hosting that is shown. The Mons trans has a long history and stems from the reliquary holders who are on the altar (between the candles in) relics of Saints exhibition in the Middle Ages. The Mons trans was used mainly during a separate ceremony in honor of the Holy Sacrament on the Sunday afternoon and during sacramental processions. The Mons trans is best known for the robbery of a Mons trans at the beginning of 2013.
Images of the Monstrans roof in the Catharijne convent [YouTube] oePSFztK9to [/youtube]