Closures can utilize lacing with eyelets, zippers, straps with buckles, or combinations of all three. Ferrules are also often referred to as eyelets or grommets within the manufacturing industry. They are almost always black, although they often feature coloured stitching and eyelets. The belt has a blackened metal buckle and three rows of eyelets. With the advent of metal eyelets, tight lacing became possible. The crown may be vented with eyelets or small mesh panels. A straight overcast stitch is used for finishing edges in eyelets and cutwork. Eyelets in the top row were usually used for connection of the suspender hooks. The middle row of eyelets accepts the size adjusting hooks. Drainage eyelets are provided in the bottom of the main compartment and the outside pockets. The eyelets are intended as ventilation holes. They may sport rudders, fins, bulkheads, seats, eyelets, foot braces and cargo hatches. Mounting a bike rack is possible without these eyelets, but requires additional hardware. Eyelets may be used purely decoratively for crafting. Solovair products come in a variety of styles, colours, and number of eyelets.