Identifying bolt thread

[bedouin]

I had an accident over the weekend which ended with a nut disappearing into the depths of the bilge never to be seen again.

As a result I have to try to identify the thread to obtain a replacement, based on scanty data.

The boat is of 1972 French construction, and the nut is probably original.

Measured with calipers the diameter of the bolt thread is 8.7 mm, and the thread looks like a fine pitch. I'm trying to find out what the thread may be so that I can either source a new nut, or at least have a better idea of the options so that I can make more accurate measurements.

8.7mm is almost exactly 11/32" - but it is probably too close for that to be the official diameter, and I can't find any major thread that has a 11/32" gauge.

Anyone got any ideas?

 

[Freebee]

this may help- thread tables:


http://www.colinusher.info/Livesteam/mewdata.html

 

[bdsweeting]

Any chance of using a magnet on a string to recover the offending item ?

 

[JackFrobisher]

You can buy a ... thing ... from Halfords, which might save a lot of searching for the thread details. It looks like one of those pipe bending springs that Plumbers use; two feet long and about 3/8 inch wide. Cunningly concealed inside is a device that has three "fingers" that can be extended to grab things in deep places. There is also a similar-looking spring with a magnet at one end. Either might retrieve the fallen nut.

 

[davehu]

Since it is a french boat I suspect it could be a metric bolt. I assume it is a solid bolt and not part of the fuel system or other pipe work. If its a solid bolt bolt I would go for an M9 thread with 1.25 mm pitch that is 4 threads per 5mm of thread length. If its a pipe union then maybe its 1/8 bsp which has outside dia of 0.383 inches and 28 threads per inch that is about 5.5 threads in 5mm.

Often an engine will have more than one nut of a similar size, if you can see one try that one and then you have a sample to take to a motor factors etc.

Hope this helps

 

[TheoSr]

As your boat is French a metric thread is likely.
There used to be an M9 (not a preferred size, but it existed) metric size as follows:
Outerdiameter 9.000 mm
Core diameter 7.466 mm
Pitch 1.25 mm

(rub a piece of paper on the bolt so that you can measure the pitch)

Keep smiling,
Theo

 

[Gordonmc]

If all else fails take the bolt to an agricultural engineers. They have a far bigger range of fixings, having to deal with odd units from all over the place, unlike motor factors.

 

[Lakesailor]

Or a specialist nut and bolt Factor. Most cities have them.
If you'd put your location in your profile, someone would probably know somewhere nearby to point you at.

 

[bedouin]

Thanks for the suggestions.

Retrieving the nut is highly unlikely - it slipped through a small crack into a part of the bilge to which there is otherwise no access without major surgery (underneath the shower tray).

Anyway the reason I was taking it off was that it was so rusty that it needed replacing - as it was a mild steel nut on a brass thread (!) I suspect that it was not original and that the last owner had trouble matching the thread. So recovering the old nut may help a little on thread identification, but not solve the problem entirely.

The pitch is fine - significantly finer than ISO Metric, probably in the 25-35 (per inch)

 

[tyce]

i find this a handy link, it has all the threads known to mankind listed, and as long as you can find exact teeth per inch and dia, it should give you the solution.
its helped me out many a time

 

[DavidTocher]

It could be a brass thread. These use the same pitch for all diameters. I think it is 26tpi but I could be wrong. My Vire BVR (made in Scandinavia) had brass thread fitttings with 26tpi threads.

David

 

[LadyInBed]

/forums/images/graemlins/shocked.gif On a boat of Bedouins age the bolts were probably hand forged /forums/images/graemlins/grin.gif