These small copper caps contained a compound that when struck by the hammer of a musket caused a spark. This spark ignited the powder in the barrel of the gun causing it to fire. Percussion caps were carried in a cap pouch worn on the belt.
A person placed on guard duty at the front lines. The picket post, like the one pictured, was positioned to be the first warning in case of any attack. If a soldier on picket duty saw the enemy approaching, he would fire his rifle to warn the men in the trenches.
The number three man of the cannon crew would insert this priming wire into the vent after the round had been shoved into the end of the cannon, and prick through the wool cartridge bag into the powder. This motion would expose the powder for ignition of the gun. One end was sharpened to a point, the other bent into ring form for easy handling.