Something like this lets you connect 2 x pieces of 20mm pipe: Masters Home Improvement
Make those pieces of PVC pipe small enough and it's just going to extend.
There's an end cap for one end and then you just need the final piece for output.
Extendable, modular and more importantly for prototypes: darn cheap.
http://www.masters.com.au/product/900004873/pvc-valve-socket-20mm
This piece has external threading on the end.
Links are to local Aussie suppliers but America has even better access - check out "furniture grade PVC" as they have a lot of different connector types.
RamJam:
Each LED is independantly controled to do pretty much anything you wish them to do. Such as flicker like a candle, flicker like a guttering lamp, flash, fade in and out, be of a particular colour, and have variation in brightness. Or have it set as colour temperature adjustable, so that it only puts out light where the spectrum is weakest.So, depending on your requirements you need to choose what sketch is to be downloaded to the candle.
Now, I can think of dozens of permutations, applications and uses that this candle could be put to. However, I don't want to have to keep redesigning brand new enclosures every time a new upgrade comes along. And I want it to be backward compatible with the battery box, and other modules.
I think for a user it isn't very practical to have to upload a new sketch each time they want the Magic Candle to do something different.
Maybe it would be better if in your sketch you can write all the different permutations or patterns that you like, and then you can add to the enclosure a couple of buttons (or it can even be made with you IR remote) to let the user cycle and chose the permutation they wish.
aarondc:
Something like this lets you connect 2 x pieces of 20mm pipe: Masters Home ImprovementMake those pieces of PVC pipe small enough and it's just going to extend.
There's an end cap for one end and then you just need the final piece for output.
Extendable, modular and more importantly for prototypes: darn cheap.
Hi aarondc. Thanks for that. So I checked the website and then googled acrylic tubing, and came up with plastock.co.ukwhich sold
Pitty it's only sold in 2 metre lengths. So I drew something based on those dimensions cut to a shorter length:
So I want everything to go into that width so as to be compatible with off the shelf candle holders.
This is a drawing of a D-cell; 
Putting the tube over the cell approximates to this; 
So there needs to be something to support the cell within the tube, idealy this would be a perfect fit but there wasn't one. Though clearplastictube.co.uk. They sold tubes in shorter lengths but not the blue one with that particular pipe wall thickness. 
with an inside dia of 34mm and outside dia of 40mm gives a 2.5mm gap which could be filled in with epoxy resin.
Next there needs to be a washer which can be cut from 5mm acrylic sheet and have a 10mm hole drilled in centre for the +ve terminal of the battery to poke through.
So I've ended up basicaly with this so far as an idea.
Unfortunately the 2.5mm gap left between the inner tube and outer tube is too narrow to insert a solid rod of reasonable diameter, which would be tapped at both ends with an M3 or M2.5 thread bore. Such a rod would need to be at least 6mm in diameter. One solution is to do away with the inner tube and replace it with an epoxy moulding like this:
The problem then becomes, how to make a moulding to form this part. The outside of the mould can be formed using the outer tube, while the inside can be formed using the outside diameter of a tube diameter which corresponds to the diameter of the cell, though slightly wider.
Next, there would need to be a base upon which the epoxy could set, such as a disk of plastic glued in place, though sufficiently brittle to remove after the resin has set. The inner tubing would have to be supported to occupy the centre. This could be done by glueing it to the disk.
