There’s more to that small usually circular or wavy shaped silvery hole that protects a curtain. Consider that the eyelet can help to enhance the beauty of the room or throw it off balance.
A strong eyelet will be flared or collared to prevent abrasion or tearing to the curtain with or without a valance. Of metal or strong plastic, rubber or wood or some material that matches the curtain and the room, it is punched in place with either a hammer, or some machine. It must be durable to be able to protect the fabric of heavy draperies and to withstand wind or the closing or opening of the curtain.
And it must conform with aesthetic requirements because a curtain must be decorative. Therefore an eyelet must mix and match with the fabric of the curtain. Eyelets can be silver-colored or stainless steel which are both neutral but contrasting, or of some color that will blend with the motif of the place; small or big depending on the length of the curtain or whether the curtain is to be installed in a room with low or high ceilings; circular, rectangular or wavy shaped depending on the shape, size and color of the curtain and room and the taste of the decorator.