I know that Toilet seats come in two shapes: round and elongated.

Yet, I have a ZI-ONE30 labelled toilet bowl, which really is a rebranded Kohler. And it's dimensions are different from all other bowls I have seen.

All my toilet bowls have 18.5" elongation, and 5.5" mounting spacing. And the bowl inner measurements for all my other toilets are 10" wide, 13.5" deep.

Yet, this specific bowl has an inner bowl size of 12" x 14". The bowl measures 17" at its (outer) widest point.

Now I am trying to find a seat for it, but all seats at Home Depot are too narrow.

The porcelain has a product number stamped into it: K3420. When googling that, I strangely find different looking bowls, as mine is a one-piece that looks very much like the Kohler San Raphael model, but it has a 1.6 gallon flush instead, and a different product number.

How can I source a toilet seat that is not only elongated, but also wider than standard?

non standard measurements

  • Where did you find that number? Take off the tank lid and list every number and letter that is stamped/cast into the inside of the tank. Feb 17, 2019 at 0:43
  • My grandmother had one of those I don't remember the brand but we got the model number from inside the tank and my brother found one by calling the mfg.
    – Ed Beal
    Feb 17, 2019 at 2:16
  • The number "K-3420" is the one that was stamped inside the tank. Along with: Complies with ASNE A112.19.2-2008 / CSAB45108. 1.6GF. Also some heraldry shield with "UPO"? And a hard to read serial no.
    – Bram
    Feb 17, 2019 at 2:54


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