Replacement opening cover for the back of a CPC scope

[AlistairHowie]

Just a quick question. The threaded opening on the back of my new CPC 1100 OTA is covered with a rubber dust cap, but it seems prone to falling off as it does not thread on .. .the thread is for the visual back.

Is there such a thing as a threaded cap that I can buy for it? I don't know the dimensions of the opening as the scope if back with David Hinds to fix an abnormal noise during slewing, but I think it might be 3.25" or so.

I can't leave the visual back on and put a cap on that because it won't fit in my Stanley 50 gallon job chest with it on. So I'm looking for something small to screw directly onto the OTA. Any thoughts? Also, is it normal for the rubber cap to be insecure, or is that just my nad luck again?

Many thanks.

[Astroegg]

If your back is like mine, you will have the large 3.25" back, and screwed onto that the slightly smaller 2" back, which has the hole. If you can cut a piece of circular plastic (like a disk or a coin if you like) to fit in the 2" diameter, place it between the 3.25" part and the 2" part which will clamp it in place, and seal the hole, whilst keeping minimal profile on the back of your scope so you can fit it in the case.

[AlistairHowie]

Many thanks for the suggestion. I came across this item, which is what I was looking for ...

Blue Fireball End Cap (External) with SCT Female Thread [#D-04]

[Astroegg]

Yikes, $20 for as dust cap! Looks well built and very up to the job, but why do we see our hobby as something that needs so much money spent on it. I would probably buy this, crazy that I am!