Disclosed herein is a centralizer for being mounted around a centralizer sub body to form a centralizer sub. The centralizer comprises first and second opposing end collars arranged, in use, to be positioned around a longitudinal axis of the centralizer. The centralizer also comprises a plurality of spring bows extending from the first end collar to the second end collar. The first end collar may comprise first and second end regions arranged, in use, to face one another. The first and second opposing end regions may comprise first and second engaging elements respectively. The first end region may be configured to be connected, in use, to the second end region via the first and second engaging elements. Also disclosed is a centralizer sub and an engaging device for use in forming a centralizer.