Tank Fit

Kohler

Wellworth and the older 2-inch Kohlers: the universal aisle mostly works here

Before Class Five, Kohler's workhorse tanks — Wellworth being the most common name on the lid — used a conventional flush valve with a 2-inch flapper and a standard ballcock. These are the Kohlers where generic parts genuinely fit. The trap is assuming every Kohler works this way.

First: confirm you do not have a Class Five

Kohler sells both designs side by side, and the tank shapes look similar from the outside. Lift the lid:

  • A rubber flapper on a hinge, covering a roughly 2-inch opening: conventional tank — this page. Measure across the drain opening to confirm; the method is on flapper size.
  • A tall cylinder (canister) that lifts straight up, no flapper: Class Five. Stop here and go to Kohler Class Five — nothing below applies to that tank, and a universal flapper will not seal it.

The K-number stamped inside the tank settles it. Kohler's parts documentation lists every internal per tank number and production year — see reading the tank stamp if the characters are faint.

What fits a conventional 2-inch Kohler

Good news: the Wellworth-family geometry is close to industry standard. A quality universal 2-inch flapper seals well on a clean seat, and a standard bottom-entry fill valve fits once you confirm the tank height. Two Kohler-specific wrinkles:

  • Some older Kohler flappers use a center-post or shark-fin mount rather than side ears. Check how your old flapper attaches before assuming the universal's ear clips will work.
  • Older 3.5 gpf Kohlers (pre-1990s) flushed on volume, not tuning. An adjustable-flapper set to drop early saves water but weakens the flush these bowls were designed around. Leave the flapper stock-timing on these or accept the trade-off knowingly.
Korky 2-inch universal (54BP class)Quality universal 2-inch flappertypically $6–$12
Fits
Wellworth and other conventional 2-inch Kohler tanks with a clean, smooth seat and standard ear mounts. Silicone versions hold up better in chloraminated water — see the hard water page if your last flapper died young.
Does not fit
Class Five canisters (no flapper exists to replace), tanks with center-post flapper mounts unless you buy the matching style, and any tank where the seat is scored — fix the seat first.
Look up current price (affiliate)
Fluidmaster 400AUniversal fill valvetypically $10–$18
Fits
Conventional Kohler two-piece tanks with a floor-to-overflow height of roughly 9 inches or more — the Wellworth family comfortably clears it. Measure anyway; the chooser on the fill valves page walks through it.
Does not fit
Kohler one-piece and low-profile tanks (San Souci, Santa Rosa) where the height runs short, and anything Class Five where you are actually chasing a canister seal, not a fill problem.
Look up current price (affiliate)

Does-not-fit notes

  • GP1083167 is not for this tank. That part is the Class Five canister seal. It comes up in every "Kohler toilet parts" search and fits nothing in a conventional Wellworth.
  • Kohler-branded 2-inch flappers are fine but not required here — unlike the Class Five, the conventional tank's geometry is standard enough that the universal genuinely performs. Spend the savings on a decent fill valve.
  • Do not mix eras. If the tank stamp shows the internals were revised across production years, order against the K-number's parts diagram rather than the part that looks right in the photo.

New flapper and it still leaks?

On a Wellworth-age tank, the flush valve seat has decades of mineral wear. If a correct new flapper fails the dye test within days, the seat — not the flapper — is the leak. See flush valve seat repair before buying flapper number three.

Next, in the tank