Button fly

What it is

A fly is the overlapping opening at the front of a trouser. A button fly closes it with a column of buttons through buttonholes on a facing; a zipper fly closes it with a zip sewn into the same opening. Both hide behind the same outer flap.

Why it was chosen

For the Standard Issue Jean the choice is buttons, for reasons that are about the life of the garment rather than tradition for its own sake:

• Nothing to fail that cannot be replaced. A zipper that jams or loses teeth means unpicking and replacing the whole zip. A tack button that fails is cut out and a new one set in a minute.
• It lies flatter. A zipper is a stiff strip; buttons and a cloth facing move with the cloth around them.
• It breaks in with the rest of the jean. The fly softens and the buttonholes ease. A zip stays a zip.

The cost is real: a button fly is slower to do up, and a raw, stiff jean makes it slower still for the first weeks. That is accepted.

How it is built here

The jean uses a 17 mm tack button at the waistband and 14 mm buttons down the fly — see Hardware. The buttonholes are worked through the fly facing, and the base of the fly, where the two sides of the opening meet the crotch seam, is reinforced with a bar tack, because that point takes the strain every time the wearer sits. See Reinforcement and bar tacks.

What it changes

Functionally: a repairable closure and a flatter front. Visually: nothing, until the jean is undone — which is the point. Over time the buttons darken and the buttonholes soften; both are normal and neither needs attention.