Full length 1/2" BSP nuts?

[Ian_Edwards]

Strange title

I'm modifying a grab rail over a binnacle to take a MFD.
I've used 1/2" A4 SS weld stubs as the "bolts" to go through the GRP to make getting the cables through easy.
I've got some 1/2" BSP back nuts and M22 washers (22mm seems to be clearance diameter for 1/2" BSP pipe).

Two questions:

Will I lose very much strength by using back nuts instead of full nuts, will adding a second back nut help?
And
Is it possible to buy full length 1/2" A4 BSP nuts, I can't find them online at the usual suspects.

As a grab rail it could have a heavy person swinging on it in heavy weather, the GRP plus backing is 35mm thick and in its original form it had 16mm bolts with just a very small hole drilled through the centre, and full length nuts, I've cut the bolts off and had the weld subs welded on.

 

[Poignard]

I would be tempted to use a flanged back nut like this

https://www.advancedfluidsolutions.co.uk/12-bspp-flanged-brass-lock-nut-6647-p.asp

Taps seem to withstand being swung on.


Or a threaded socket:

https://www.bes.co.uk/screwed-full-...MI4fyp7vj-4AIV0YeyCh1UjwcAEAQYASABEgKqGPD_BwE

 

[Ian_Edwards]

Thanks for the suggestions, I couldn't use a socket, the access is very difficult, I'll have to use a box spanner to tighten, I can't get my hand to one of the legs, it's obstructed by the steering gear.

The flanged back nut looks like a possibility, I assume that it is longer than a standard back nut, so has more threads, although I'll use M22 washers to help spread the load, However, I can't find a SS version online, lots of brass and bronze.

 

[colhel]

Why can't you use bronze nuts? Be much stronger than ss

 

[Ian_Edwards]

I don't really understand that comment, The UTS of stainless and silica bronze are about the same, around 575 MPa for SS and about 585 MPa for silica bronze.
So assuming the same size nut, there wouldn't be much difference.
If I use a bit of copper grease on assembly, I should avoid the potential galling with SS.
A bronze, SS mix will give me a dissimilar metals problem.
And I don't know if it'll be much easier to find a 1/2" BSP full sized nut in silica bronze than it is to find a SS one.

 

[Poignard]

A bronze, SS mix will give me a dissimilar metals problem.

What problem? Your bronze propeller is mounted on a s/s shaft and you don't worry about that.