Markwort 12 Color Coded 5 oz. Weighted Softballs (SBWT5) These are 12 Softballs with Split Leather Cover, Weighted Cork Core, and White Stitching. As You Train, Gradually Increase the Weight of the Ball as You Build Strength in Your Throwing Arm. Color Coded Cover Indicates the Ball Weight. Available in 4 oz., 5 oz., 6 oz., 7 oz., 8 oz., 9 oz., 10 oz., 11 oz., and 12 oz. Weights (A Regulation Size Softball is 12 and Between 6.25-7 oz.). Color/Size: Markwort 12 Columbia Blue - 5 oz.