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Thru-Hull 3/4", Mushroom, Threaded

Part #: Z1808
This National Pipe Straight Mechanical threaded mushroom style thru-hull is used in several locations to replace the sub-standard original equipment thru-hulls in early Catalina sailboats. Locations include sink drain and head intake in a wide variety of boats, from the Catalina 22 to the Catalina 42. It is also a favorite to upgrade the scupper thru-hull fitting on the first generation Catalina 22.
Early Catalinas including the Catalina 22, Catalina 25, Catalina 27, and Catalina 30 used a simple bronze pipe nipple for a thru-hull fitting. It was glassed into the hull with a garden variety gate valve threaded on top. It relied solely on the adhesive characteristics of the polyester resin to bond the pipe nipple to the hull. This weak bond is all that is between you and the bottom of the sea!

The old pipe nipple "thru hull" is not recognized as an appropriate installation by any marine standards authority. And any surveyor worth hiring will advise they be replaced immediately.

Use this glass reinforced nylon replacement in any of the above locations. It is made from the same material as thru-hulls in new Catalinas and many other well recognized manufacturers. When properly installed, it is approved by the American Boat and Yacht Council. Installation requires a 1" hole saw.

You will also need a replacement valve and the appropriate hose barb fitting shown below. Replacement is easy. Remove the old valve and pipe. It will likely be so easy it will scare you. Reinforce the hull and complete the upgrade using step by step instructions included with our thru-hull installation kit.
Molded Marelon offers superior strength and corrosion resistance. Marelon is lightweight, corrosion and electrolysis free, ideal for thru-hull valves. Marelon is a modern material formulation of polymer composite compounds that uses resins and additives to produce an extremely strong marine-grade product that will not deteriorate like traditional bronze marine plumbing parts. All Thru-Hull Connectors must be installed with proper bedding compound. We recommend a maximum torque setting of 20 lb/ft. Ideal for above and below the waterline applications.

National Pipe Straight Mechanical (NPSM) threads used in marine fluid systems that requires thread compound or Teflon tape to seal. The female component incorporates a straight, non-tapered thread with an inverted 30° chamfer of the male connector on the seat of the female. This is a mechanical seal.
• Thread type: 3/4" National Pipe Straight Mechanical (NPSM)
• Outside diameter of thread: ~1"
• Outside diameter of flange: 2-1/16"
• Length overall: 2-9/16"
• Thickness of head: 5/16"
• Length under head to end: 2-1/4"
• Length of thread: 1-13/16"
• Thickness of nut: 9/16"
• Maximum usable length (flange to flange nut): 1-11/16"
• Minimum usable length (flange to flange nut): 7/16"

Technical Support

Through Hull Evolution - Caution Vintage Catalina Owners!
To change or not to change? Don't let that question keep you up at night, but pray it is not water waking you in the morning.
Pipe Sizes and Why They Are So Confusing
Why doesn't my 3/8" NPT fitting measure 3/8"?