David Tyler wrote:

So, is the outside diameter 145, and not 150? Quite likely, as there is a Nedal tapered tube at this size. If so, I'm not so sure that it's a good idea to use it.

If it is indeed a Nedal tube, is the next size up available, 165mm? That's the size that I have. If so, your troubles are over.

No, it's not a Nedal tube, but a finnish-made one :/


Oh dear, back to square one.

David, you were indeed right - the flagpole has 2,8 meters of straight tube at the lower part. 

However, the inner dimension is 140mm or a tad under it, so there is no way of inserting a 140mm tube in. And the next diameter available is 130mm. 

Do I have other options to strengthen the lower part? A wooden inner mast?

(Or getting a 140mm tube done to 139mm by a machinist, which I'm afraid will be expensive considering that I have to buy 6000mmm of the 140mm tube anyway. Is it possible to do this with home tools yourself?)

Generally, these flagpoles are parallel for a third to a half of their length, and then they start to taper, so I was thinking that at least a 4m length of internal sleeve was possible, if thought desirable.

David Tyler wrote:

Sorry, I don't think the flagpole is enough on its own. But if you were to take a length of 140 x 4 tube (maybe 3m long?), add a seal at each end that was guaranteed leakproof  to fill the 2.5mm gap (maybe some self adhesive foam rubber strip?) push it inside, drill a hole and pour in polyurethane casting resin, then I think you could end up with a very good mast. Strong and stiff at the bottom, light at the top.

Hmm - and sorry. I'm sure it's me and not your text, but I don't seem to get the idea. Do you mean that this straight tube is inserted inside the flagpole or vice versa? Or something else?

It seems that there are tapered aluminium flagpoles available here. The length is 12m and the diameter ranges from 150mm to 60mm, but the wall thickness is only 2,5mm. I suppose this is not enough, even I could cut 2 meters off from the top?