The acorn sword knot is a decorative and functional accessory used in the military for securing a sword or bayonet to a soldier's wrist or belt. It typically consists of a looped cord with a tassel or knot at the end, resembling an acorn. The primary purpose of the sword knot is to prevent a weapon from being dropped during combat or other activities.

Historically, sword knots were widely used in various armed forces around the world, especially during the 18th and 19th centuries. They were often made of leather, silk, or other durable materials. The design and material of the sword knot could vary depending on the specific military tradition or regiment.

In modern times, the use of sword knots has diminished with the decline of traditional edged weapons in most military contexts. However, they may still be used for ceremonial purposes or by reenactment groups that focus on historical military practices.

If you have a specific question about a particular type or style of acorn sword knot, or if you're interested in a particular military tradition or historical period, please provide more context, and I'll do my best to assist you.