Okay, so you're making sinks now, but you can't figure out how to get the drain to sit in the bottom correctly. That's where this little kit comes in. Containing a 1-3/4 inch core drilll (also available seperately) for the drain hole and a diamond plated coutersink for angling the top of the hole for the drain (fits holes 1-1/2" to 2-1/4". The countersink can also be purchased seperate from the core kit.