Which of the following is used as a cleaning or maintenance tool for muzzleloading firearms?

The nipple wrench is specifically designed for cleaning and maintenance of muzzleloading firearms. This tool is used to remove the nipple, which is the small piece that holds the percussion cap. Proper maintenance of the nipple is essential for reliable ignition and overall functionality of the firearm. By ensuring the nipple is clean and free of debris, the user helps to prevent misfires and ensures the firearm operates safely.

The other tools listed play supportive roles in the cleaning and care of muzzleloading firearms but do not directly relate to the specific function of removing and cleaning the nipple. The push rod is typically used for seating the projectile, the cleaning brush is essential for cleaning the bore, and the rammer assists in pushing the projectile into the barrel. While all these tools contribute to the overall maintenance of the firearm, the nipple wrench is uniquely suited for managing and maintaining the nipple, making it the correct choice in this context.