American Standard 735004 Color:Black We are not positive but

We are not positive but believe the hole is used for some kind of locking mechanism

Tank Size: 18" x 10

Manufacturer: AMERICAN STANDARD

It hardens to a consistency similar to automotive paint and is chemical resistant so you can clean it with normal household cleaners

Tank Size: 16

American Standard 735004 Color:Black We are not positive butManufacturer: AMERICAN STANDARD Lid P N: 2012 735004 Lid Size: 20" x 8. 625" Tank P N: 2037 Tank Size: 19" x 7. 5" Toilet Model: Roma II One Piece This is also a Lexington toilet, often confused with 735025. Check to make sure you are ordering the correct one based on the photos and dimensions we have listed.