Men's dress shirts often have a loop sewn onto the back of the collar to help keep the bow tie loop in place. Loops are most frequently featured on high-quality dress shirts that are worn for black- or whit-tie events.
The loop also ensures that the bow tie will not come unraveled while being worn. If a shirt has a loop, the bow tie should be put through the loop before it is tied.
The bow tie originated during the 17th century, when it was worn as a scarf around the neck to hold together the opening of shirts. Sizes range from about 14 to 20 inches, much like shirt collars. Bow ties can be worn with wing-collar shirts, which hide the clasp of an adjustable bow tie.