This is a Weller 2-pack Replacement Brass Wool Sponge Tip Cleaners. Its part number is 0051384099. The Weller 0051384099 is a replacement set of metal wool balls to fit into the WDC Dry Cleaner. Wiping hot iron tips on wet sponges produces thermal shock on the tip plating, prematurely wearing or possibly cracking the plating. Weller's WDC Tip Cleaner safely cleans soldering tips using a special metal wool ball which removes oxidation from the tip with no thermal shock. Weller 0051384099 is a pack of 2 replacement metal wool balls for the 0051512499 WDC stand.