We don't yet know the diameter of the holes so we can't compare them to extenders or sleeve nuts.
but we do know
but we do know
S
SammyInnit
I simply don't agree. Threaded rod as it's used for the majority of commercial building services installations has to meet a BS-EN standard for certification and sale. I believe the tests for 8.8grade mild steel/zinc plated are nominal 800n/mm².
Without going through the calculations of the very rare occurrence of say a 40mph+ wind speed in the UK and it's probably going to be no bigger than 4' in height (let's say 6' for good measure), I'm confident in saying M6 threaded rod is more than adequate although that's not to say it would be my first choice, I'd prefer M8-M10
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Remember Sammy, this is a DIY site and most users are going to get stuff from places like B&Q, where it often will not fully meet standards but will in fact be the cheapest crap they can find that they then sell for the same price as decent stuff, it will also depend upon how many are used.
As for 40mph+, try 60mph+, we are having some bad storms these days.
Raising the lamppost up by putting it on something, a plinth, a slab with holes drilled in it etc. will then allow for M8 threaded tubes to be used which can then have M8 bolts going down into them.
i.e.
https://www.screwfix.com/p/easyfix-...r5PFszjzHEzqch6dkORoComkQAvD_BwE&gclsrc=aw.ds
Which IMO would also be aesthetically better than threaded bar and nuts.
As for 40mph+, try 60mph+, we are having some bad storms these days.
That's almost exactly the same as what I said, steer clear of M6
Raising the lamppost up by putting it on something, a plinth, a slab with holes drilled in it etc. will then allow for M8 threaded tubes to be used which can then have M8 bolts going down into them.
i.e.
https://www.screwfix.com/p/easyfix-...r5PFszjzHEzqch6dkORoComkQAvD_BwE&gclsrc=aw.ds
Which IMO would also be aesthetically better than threaded bar and nuts.
S
SammyInnit
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I had another thought about this while walking the dogs but this needs the Op to get his ass back here and post!
Photos of the lamppost and base are needed, however;
Can the post be rotated 45 degrees? If so just accept the cockup and grind the bolts off, drill 4 new holes for BFO rawlbolt type bolts (or a better version of that type of thing).
OR just offset it a little so new holes can be drilled.
If that idea suits then I'd make a cardboard template with the existing studs having holes, so I can mark and drill new holes "before" grinding the existing studs off, just in case the new holes don't go well.
Photos of the lamppost and base are needed, however;
Can the post be rotated 45 degrees? If so just accept the cockup and grind the bolts off, drill 4 new holes for BFO rawlbolt type bolts (or a better version of that type of thing).
OR just offset it a little so new holes can be drilled.
If that idea suits then I'd make a cardboard template with the existing studs having holes, so I can mark and drill new holes "before" grinding the existing studs off, just in case the new holes don't go well.
Sorry I was out boozing on cask ale Friday then making the most of the sun all weekend!
Really appreciate all replies and they have helped me -- essentially the M8 thread I supplied was sunk too deep into the concrete so (ideally) I needed a way of extending it. The only thing holding me back on this was the length of the reducing connector as I wanted to try and find a smaller one rather than sawing. Now I know it's probably going to be easier to saw rather than source, I am doing this. The thread should then protrude around 8mm beyond the base of the post in order for a capping nut to fit on -- none of the threaded rods are seen as previously explained so this...
Considerations have already been made for environmental conditions -- the post will be very safe where it is!
@mattylad -- I think you mentioned the DIY sheds about 3 times! Although it's totally irrelevant to the post, the posts were actually sourced indirectly from a contractor who supplies to business only. In short i bought from my employer as they are being installed in one of the employee gardens. The price of them lowered when the order quantity was increased so a few of us had one.
Soon as it's up in late-April I'll try to remember to come back and post pics!
Really appreciate all replies and they have helped me -- essentially the M8 thread I supplied was sunk too deep into the concrete so (ideally) I needed a way of extending it. The only thing holding me back on this was the length of the reducing connector as I wanted to try and find a smaller one rather than sawing. Now I know it's probably going to be easier to saw rather than source, I am doing this. The thread should then protrude around 8mm beyond the base of the post in order for a capping nut to fit on -- none of the threaded rods are seen as previously explained so this...
...isn't an issue.
Considerations have already been made for environmental conditions -- the post will be very safe where it is!
@mattylad -- I think you mentioned the DIY sheds about 3 times! Although it's totally irrelevant to the post, the posts were actually sourced indirectly from a contractor who supplies to business only. In short i bought from my employer as they are being installed in one of the employee gardens. The price of them lowered when the order quantity was increased so a few of us had one.
Soon as it's up in late-April I'll try to remember to come back and post pics!
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Okay bit of tit head moment... I picked up the reducers only to find out they don’t fit. Reason being the rod set in concrete is actually M10 not M8 so I need to go and get an M10 to M8 reducer! 
I didn’t measure them properly with the micrometer in the first place.
I didn’t measure them properly with the micrometer in the first place.