counter
counter for long, narrow objects
Used for items like guns, scissors, candles, shamisen, oars, and similar long or slender tools. Common in traditional and everyday contexts.
はさみを一丁ください。
Please give me one pair of scissors.
この店には鉄砲が三丁ある。
There are three guns in this shop.
本 is the general counter for long cylindrical objects (pencils, bottles, etc.), while 丁 is more specific to certain tools, weapons, and instruments.
The kanji 丁 originally referred to a block or a unit, and its use as a counter for long, narrow objects developed from counting tools and weapons in traditional contexts.