Lay a piece of plastic wrap on a flat surface. Sprinkle the sharp yellow cheddar on a small plate.
Add the pimentos, cream cheese, white cheddar cheese, mayonnaise, and salt and black pepper into a mixing bowl and mix on medium speed until well combined. Using a rubber spatula, bring the mixture into the center of the bowl forming a ball.
Generously roll the ball in the prepared yellow sharp cheddar and place on the prepared plastic wrap.Wrap the pimento cheese ball with the plastic wrap.
Wrap the kitchen string across and around the ball gently pressing it into the pimento cheese. Twist the string at the bottom and wrap the opposite way across and around again. Then, twist again this time at the top down the center of the fourths. Lastly, twist again at the bottom and back up the opposite side. Tie off at the top. Place in the refrigerator for at least one hour to chill. ( See photos in post.)
Remove from the refrigerator and carefully unwrap. Place the bell pepper stem on top.