Nothing is ever straightforward ...

[Demonperformer]

I bought a pack of delrin rings (from FLO) to give me an extra couple of mm between my FLAT6 reducer and my new filter wheel (also from FLO). These two connect successfully, and both state that they are "T thread". The FLO page states that the rings will "slip over" any T2 thread. I have not been able to find a lot on the internet concerning the comparison of T & T2 threads, but this post states that they are "interchangeable" (3rd post down in the thread). So, in my naiveté, I thought the rings I was buying would slip over the thread on the reducer. Unfortunately I have been unable to get them to do so - they are just that little bit too small. And they don't seem to have sufficient elasticity to stretch.

One thought I have had is that I could use a stanley knife to cut them across one side. This would give me the slack to get them over the thread (by opening it slightly) and, hopefully, the lack of elasticity that is preventing them from stretching would pull them back into shape so they stay closed and do the job of providing the extra couple of mm required. However, this is a fairly non-reversable action, so I thought it would be worth checking on here to see if anone is aware of another (less drastic) method that might work and that I should try first.

Any thoughts?

Thanks.

[astro mick]

Yep I had to cut them as well, no problems with doing that, as they retain their shape, then just open slightly and slip on.

Hope this helps.

Mick.

[Demonperformer]

Thanks, Mick.

I'll get to start imaging with this scope sometime ...

[Lorne]

Would dropping them in a cup of boiling water soften them a bit to stretch them over the thread?

PS.... use long nose pliers to get them out the cup! 

[swag72]

I cut all of mine so I can put them over the thread as needed.

[andrew s]

I have used these http://www.edmundoptics.co.uk/optomechanics/tube-system/t-mount-components/t-mount-brass-spacer-rings/2761/  and have never had any issues fitting them to various T thread components.

Regards Ndrew

[Demonperformer]

Thanks for the input, everyone. I think I will pursue the 'cutting' option, as (1) I already have them, so purchasing new ones at this stage will gain me nothing if it works, (2) I suspect that if I tried heating them, then when they cooled they would be stuck solid which would introduce difficulties if I do not get the distance quite right first time.

Thanks.

[martin_h]

I've had 2 sets of the rings and none of them "slip over" I've always managed to force them on, but getting them off is a different story!

[Demonperformer]

Yes. And I think getting them off could be an important part of the exercise. Firstly, I have calculated that about 2mm is the right extra distance, but I will try it and will then want to be able to make appropriate adjustments depending on the results. Secondly, I understand that the distance will alter depending on whether or not I am using a filter, so it will need to be "variable".

Thanks.

[RichLD]

+1 for cutting them 

[DaveS]

So it's not just me then. I have a set from FLO with the same problem and just wrote it off to experience. I still have them somewhere so may be able to make use of them with the aid of wire cutters.

[Demonperformer]

Well, for good or ill, there's no going back now ... two of my 1mm rings have been cut. They now fit quite snuggly on the reducer. So, next clear night it will be go out and see how close I am to the required distance.