Deck fill cap

[Don Crossley]

Hello,

I'd like to buy a spare deck fill cap for water/diesel tanks. My cap is 1-5/8 dia at the threads and 1-3/4 at the top. In the local marine store and online, I have not been able to find a cap that fits. They all seem to be 1-1/2" or 1-3/4" dia at the threads, and the thread count on my cap appears to be higher (finer) than the ones I see in the store. The deck fill fittings of course have no brand name to help figure this out.

Does any know what caps will fit or brand name of the original deck fill fittings?

Thanks for your help,

Don

'87 NS30U

Vancouver, BC

[Tom Schoenhofer 26C#28 North Star Penetanguishene]

Hi Don

On my boat the diesel cap is the same as the 3 others on the water and waste fill openings. This Binnacle part looks just like it. I have a plastic plumbing nipple with a 1 1/2 NPT thread that screws right into any of these.

The 1 1/2 inch threads are a little larger than the nominal 1.5 inches. I have a table that says the OD is 1.79 and the pitch is 11.5 threads per inch.

https://ca.binnacle.com/p7689/Stainless-Steel-Deck-Fill-for-1-1/2%22-Hose/product_info.html#description

Tom

26C #28

Penetang

[Don Crossley]

Hi,

Thanks for the reply and info. If the plastic plumbing cap is 1.5" dia, then its too small.

Don

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[Paul Miller]

Could you be confusing actual measurements with pipe thread sizes? A 1 1/2” fitting is a fitting with a 1 1/2” pipe thread which is the thread on the outside of a pipe that has an inside diameter if 1 1/2”. The thread is quite a bit bigger. Deck fittings are all pretty standard and on boats the size of ours are almost always 1 1/2”.

Paul M

NS30U #211, Sandpiper 

Cowichan Bay B.C.

[Mariner's Cat V 26C Brentwood Bay BC]

Always , but not always.... Benaslow uses metric threads..... I replaced my fittings with a winch type key slot and they are metric.  Not a big issue but had to get a fitting machined for the head discharge, which I now no longer need as we use a composting head.

But 99% are 1.5 pipe

[Tom Schoenhofer 26C#28 North Star Penetanguishene]

That's right. 1.5 inch pipe is the pipe ID. The thread OD is larger, 1.7 or more than 1.8 depending on where you measure.

My 1.5 inch pipe nipple, 1.5"NPT, is part of a plastic mushroom that is now used for the composting toilet air vent. 

Pipe size is the ID , tube size is the OD. Another thing I have leaned on this list.

Tom

[Don Crossley]

Hi,

Ah... no. The outside diameter of the threaded portion of the cap is 1-5/8", The top of the cap is where you put the key to open it is 1-3/4". I bought a Seadog temporary emergency plug designed for deck fillers, but it is only made for fillers up to 1.5" ID, and it was too small for my filler fitting, so returned it.

I may have found a plumbing fitting that will work, but have gotten plumbing store yet to pick-up. Will do so tomorrow.

Thanks,

Don

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[Ward Woodruff]

The O.D. of 1-1/2” pipe is 1.9”. 

Ward Woodruff

N33 #8 Margery

Niantic Bay, CT

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On May 4, 2021, at 2:28 PM, Don Crossley <doncr...@gmail.com> wrote:



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[Don Crossley]

Hi,

Okay, I bought a black ABS pipe cap at plumbing store, it is a fitting meant for a ABS 1-1/4 pipe system, commonly use in construction for drain, waste, or vents (aka "DWV"). It's description stamped on the cap is a DWV 1-1/4", a plug with MIPT threads. Although the threads appear courser than my stainless cap, it seems to fit securly. I just want a spare for "emergency" use, in case I'm away somehwere and accidentally drop the cap overboard... yes I've done this before on a different boat.

And for those of you who wondered about the measurements I gave before, please see photos below.

Cheers,

Don

'87 NS 30U #369

Vancouver, BC