The inner tube size “26 x 2.125” refers to the specifications of an inner tube used in bicycle tires. Here’s what each part of the size specification means:

1. 26: This indicates the diameter of the tire the inner tube is designed to fit, which is 26 inches. This size is common for mountain bikes and some cruiser or comfort bikes.
2. 2.125: This represents the width of the tire the inner tube is designed to fit, which is 2.125 inches. This width is relatively wide and is commonly found on mountain bikes and certain cruiser or comfort bikes.
3. Color (Black): The color specification indicates the color of the inner tube, which is black in this case. Black is the most common color for inner tubes, although they can sometimes be found in other colors as well.

Overall, an inner tube with the size “26 x 2.125 (Black)” is designed to fit a 26-inch diameter tire with a width of 2.125 inches. It’s important to ensure that the inner tube matches the size specifications of the tire it’s intended to be used with to ensure proper fit and performance.