Aqua Science • Well Water Help

By Michael Izzo

A well cap needs to fit the casing correctly. A familiar size label, such as “6-inch,” is not enough to confirm the fit.

Before ordering, gather measurements and photographs of the existing installation. This helps Aqua Science identify a suitable cap or seal without guessing from a name alone.

Measure the casing, not the cap cover

  1. Find an accessible, straight section of the casing below the cap.
  2. Measure the pipe’s outside diameter from one outer edge to the opposite outer edge. Do not use the cap’s larger cover as the pipe measurement.
  3. If measuring straight across is impractical, measure the casing’s circumference and divide by approximately 3.1416. Record that this is a calculated outside diameter.
  4. Note the casing material and any markings. Tell us if a coupling or adapter changes the diameter where the cap attaches.

Keep the well protected. Do not remove the cap or disturb electrical connections simply to obtain a measurement. If access requires opening the well, have a qualified well professional handle it.

Nominal size and actual diameter are different

The nominal casing size is a product designation, not a guarantee that its outside diameter is the same number. For example, Boshart lists certain nominal 6-inch or 6¼-inch well caps for casing with a 6⅝-inch outside diameter. Other casing and cap combinations differ, so use the exact manufacturer’s fit chart.

That is why “I have a 6-inch well” is a starting point, not a complete order specification. A cap that is too loose or the wrong style may not seal properly.

Send useful photographs

  • The top of the existing cap, including its brand or model markings.
  • The side of the casing and the area where the cap meets it.
  • A clear view of your measurement.
  • Visible conduit, wiring entrances, and plumbing connections, without disturbing them.

Also describe whether you need a replacement cap, a sanitary seal, or replacement parts for an existing assembly. These are not automatically interchangeable.

Confirm the complete fit

Outside diameter is essential, but conduit size, casing condition, cap design, and local well requirements also matter. A properly fitted cap helps protect the well opening; it does not replace water testing or repair an already contaminated well.

Email your measurements and photos to info@aquascience.net for help identifying the right part.

Manufacturer reference: Boshart well-cap fit chart

Need help with your well system?

Contact Aqua Science with your system details so we can help you compare suitable equipment.

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