This item is a crown and flint pair of lenses that will make a nice 13 mm diameter, 30 mm focal length doublet. This would be a great practice project for those who are planning to assemble their own multi-element lenses. Use our Canada balsam, or one of the several UV cure optical adhesives that are available. Go small before you go BIG! These components may have been previously assembled and uncemented with solvent, but are optically in good condition.