The tray is usually made of plastic or metal and can hold a varying number of fibers, depending on the size of the box. All retaining tabs on the tray have radius edges and rounded corners where fibre may pass. The overall dimensions of the tray are 148 x 125. A fiber optic splice tray is a component of fiber optics management that is designed to securely and efficiently store and organize fiber fusion splice and slack fibers, installed inside fiber splicing closures, enclosures, and cabinets. It is designed for installation inside: A good splice tray. An optical fiber is a single, hair-fine filament drawn from molten silica glass.