The original Lee 101Z jeans used a zipper instead of a button fly.
Lee introduced the 101Z as a zipper-front version of its well-known 101 line. The “Z” referred to the zipper construction, making the jeans quicker to put on and remove than traditional button-fly work trousers.
The design was significant because button flies had long been standard in durable American workwear. A zipper offered a modern alternative while retaining the sturdy denim construction associated with Lee. The 101Z became an important early example of a widely marketed zipper-front jean.
The 101Z is sometimes confused with later Lee models or with Wrangler’s 13MWZ cowboy jean. Those products belong to different brand histories. The defining feature asked about here is the 101Z’s front zipper.