Nuts!

TiggerToo

TiggerToo

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Tigger's seacock handles are corroding as are the nuts that hold them in place. Does anyone have any idea what sort of thread these might be and where it might be possible to obtain replacement (possibly galvanised, stainless steel or othewise more corrosion resistant ones)?

Thanks
 
If your boat is still the Dufour, then the threads are almost cetainly metric. Do you actually have seacocks, or are they just ball valves screwed onto a threaded skin fitting? If they are the ordinary plated brass ball valves, then I suggest that if the boat is out of the water you would do best to replace the ball valves with bronze or DZR brass ones rather than try to replace corroded handles and nuts.
 
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Does anyone have any idea what sort of thread these might be

[/ QUOTE ] As said by Norman E probably metric. Measure the outer diameter of the thread in mm using a vernier gauge if possible ( a micrometer if you have one). If that is an exact whole number (or an exact half mm in smaller sizes possibly) then that will be the M size. Get a nut and try it.
Otherwise post the diameter and we can look in the tables to see what corresponds. Ideally we'd like to know the thread pitch but unless you have thread gauges you wont be able to determine that (and if you had them you would not be asking here anyway).
 
Quote "If that is an exact whole number (or an exact half mm in smaller sizes possibly) then that will be the M size."

Not so I'm afraid. Metric threads have a flattened thread crest, (with some permitted rounding) and the overall diameter measured with a micrometer will be slightly smaller than nominal diameter. One point to note is that 5/16 of an inch is very close to 8mm, and this can easily lead to confusion between metric and imperial.
 
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If your boat is still the Dufour, ....DZR brass ones rather than try to replace corroded handles and nuts.

[/ QUOTE ]

yes Tigger is a Dufour, and the ball valves have been replaced with DRZ ones. The cocks themselves are in excellent condition (new two years ago) with no evidence of corrosion or dezinfication. It beats me though why they have such C**P handles and nuts. The nuts are not "M" sized: I spent some time at B&Q trying out all the thread possible there. They might well be Imperial. I have handed them over to the engineering worshops here at Imperial (College, that is) and I hope I'll get an answer on threads. It still leaves me with eth question: where to I find ss ones, or bronze ones, or properly galvanised ones..... Do you think that pasting the thread with duralac or somesuch thing might prevent corrosion? How about covering them with grease/vaseline?

Ideas welcome.
 
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overall diameter measured with a micrometer will be slightly smaller than nominal diameter.

[/ QUOTE ] but the difference will be so small that it probably wont be detected with a vernier gauge. I should have left out the word "exact", something i realised almost as soon as I'd pressed the submit button. OK you might confuse 5/16" with 8mm but the pitch of 5/16 threads is different to the metric threads (both Whitworth and UNC are coarser while BSF and UNF are finer I think you'll find) that's why, in the absence of any knowledge of the thread pitch, I suggested getting a nut and trying it.

Anyway he has, we now know, already done the sensible thing and tried the (metric) nuts on offer at B&Q. That leaves the unlikely possibility that they are fine metric threads or that they are imperial, probably Whitworth or UNC, or possibly non standard. Again half the process of determining the size will be to measure the diameter, followed by the pitch leaving only the possibility of confusing smaller Whitworth and UNC threads.

How about actually making a <u>constructive</u> suggestion or two that would help someone to ID a thread!

I am sure the technicians in the engineering department at IC will be able to ID the thread easily. More quickly than I can type this I should think!. My father worked in the engineering department of one of the London Colleges for a time. By now he'd have made the bl88dy nuts as well.
 
If its any help, I have just removed a nut from a European made 1/2 " ball valve that I have at home, it is 8mm dia x 1mm pitch, ie ISO metric fine series, ( very close to 5/16 UNF ). I would expect unified threads on valves made in the US. Metric fine series fasteners will not be readily obtainable from any but specialist suppliers.
 
In the absence of a thread gauge measure the diameter using a vernier caliper and measure the pitch using the same. If the valve is in a difficult position you could use blue tack to take a pattern of the thread and measure the pitch.
 
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In the absence of a thread gauge measure the diameter using a vernier caliper and measure the pitch using the same. If the valve is in a difficult position you could use blue tack to take a pattern of the thread and measure the pitch.

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the blutack method is an excellent idea...
it is just a pity that the valves are in a very difficult position to reach: 250M down the M4/5!!! /forums/images/graemlins/mad.gif

Still, thanks everyone, I am sure I will manage to find something with your advice.
 
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