M12 nut - imperial or other type close in size?

[Burnham_Bob]

I have a large nut and bolt securing my tiller arm. Removed the nut - reason why not relevant - but as the old nut is a nyloc one that has been on and off several times decided to buy a new one.

Visual inspection suggested M12 size and the 19mm across flats seemed to agree. But new nut won't fit. Can't get it started. Old one was difficult to start too but got it on eventually and tightened it up.

The new nut if anything is a little small. Don't want to take the old one off again in case it won't start. Any ideas of what the old nut and bolt might be?

 

[Norman_E]

All the "half inch" sizes are a bit bigger than M12, and may be 3/4" AF nut size. You have a choice of the old English sizes of 1/2" Whitworth, (12TPI) 1/2" BSF (16TPI) or American threads UNC (13TPI) or UNF (20TPI)
In addition to the above there are some special threads, but mostly fine pitched in half inch size.

If it is a 12mm Metric thread the usual 12mm thread pitch is 1.75mm, but finer pitches are available.

 

[Conrad]

If guesswork won't work you will either need to take the old bolt out and with you to the nut shop or get hold of a vernier and thread guage so you can take an accurate measurement of the bolt diameter and the pitch of the thread, the thread guage if you've not seen one looks like loads of small saws whose teeth fit into the threads, when they fit perfectly you have the right thread size.

If the nut is difficult to start you could look at the thread on the bolt and perhaps open up the initial slots with a small file or even a junior hacksaw if they are damaged and of course make sure there is no rust or other gunk filling up the remaining slots.

 

[dukes4monny]

Your really need to measure the OD of the thread (bolt) to get a good idea.
M12 = 12mm OD
12mm ISO Metric Fine = 1.25mm pitch
12mm ISO Metric Coarse = 1.75mm pitch
12mm = 0.4724"
7/16 UNC = 0.4375" = 11.11mm: 14 TPI (Threads Per Inch)
7/16 UNF = 0.4375" = 11.11mm: 20 TPI

That's not all of the possible candidates, but the most likely.

 

[VicS]

This table might be helpful HERE

 

[earlybird]

If your boat dates back to the '70's, then it is odds on that the nut is 1/2 in. either BSF or Whitworth, although your 19mm A/F dimension doesn't quite tally. These imperial size threads have been obsolescent for 40 years, and are now as scarce as hen's teeth, esp BSF. but a plain nut could be made. The readily obtainable 12mm. iso-metric size will not fit either of these imperial sizes.

 

[skenn_ie]

South Essex Fasteners on the Temple Farm Industrial Estate near Southend are excellent. They will identify the thread, and if they don't have one, they will usually be able to get it for the next day. They, and Leigh Baxter(for valves, hoses and skin fittings, I can't praise enough.

 

[Avocet]

This is a real bodger's way out and i have to stress that replaing the nut is, of course the correct way. If you're stuck, however, I find that putting the nut on a hard, flat and solid surface, then giving it a sharp tap with a hammer tends to squeeze the nylon a bit and extrudes a tiny bit more out into the hole, making it grip again.

 

[Adaero]

[ QUOTE ]
This is a real bodger's way out and i have to stress that replaing the nut is, of course the correct way. If you're stuck, however, I find that putting the nut on a hard, flat and solid surface, then giving it a sharp tap with a hammer tends to squeeze the nylon a bit and extrudes a tiny bit more out into the hole, making it grip again.

[/ QUOTE ]
I agree, the method I have used is to centre punch around the nyloc area in 3 places which will again loads up the gripping force of the nylon.
Regards
Bodgit & Scarper

 

[[448]]

Couple of points. If the old nut goes on but tight, what is the problem?
What's wrong with a squirt of loctite?
Dave

 

[Bilgediver]

Your profile refers to a Halcyon 23. If this is the boat in question as designed by Alec Buchanan then I would suggest that you are dealing with either UNC or UNF or BSF and BSW.

Westerly at this time seemed too use both depnding on the subcontractor.

You should be able to find the right nuts a a proper motor mechanic. One of those furthest from the centre of town that maybe understands Ferguson tractors as well /forums/images/graemlins/smile.gif

Like others I would think thay if a nut came off it should go back and it can be easily locked the a loctite product.