I have a number of torches with different sized diameters. I usually take my AA lights with me when I go walking.
I have previously bought a number of silicone lantern diffusers for my torches with 40mm diameter, and smaller ones with 20-25mm diameters.
While I own a few more expensive torches, I generally don't take them as my main torch while walking, as I have lost a few over the years. The 40mm torch in the pic above is a great 4xAA 860lumen torch but is a bit big for longer hikes, but I have used it in caves. So I take a few cheaper CREE LED torches that I can bare to lose. The ones I take walking now have a diameter of between 26-28mm, and my existing diffusers don't fit. This, incidentally, is approximately the head diameter of torches like the LedLenser AA series torches or the Mini Maglite AA torch, and the Aldi LED Trekking Torch I reviewed here viewtopic.php?f=15&t=20635:
So I thought I might as well share the options of DIY diffusers I have used the in the past, as well as my current option for 26-28mm torches.
PET Bottle tops (white/translucent) - these work on around 25mm torches and are ok, but don't spread the light out much like a lantern would. Works when you tail stand the torch as a candle and works ok hanging from the ceiling.
35mm Film Canisters (translucent) - these are a larger diameter, around 30mm, so if you have a larger torch it might work out, but can be difficult to procure now that 35mm film is rare. For me, on my 25-28mm torches I would use an o-ring attached to the torch. But I would constantly lose the O-ring, and the lantern diffuser would only work standing the torch in candle mode. When inverted, like hanging from the inside of a tent, it would usually fall off.
I kept looking for the perfect DIY diffuser, and I noticed that Berocca style/effervescent tablet tube containers seem to have the perfect diameter. I am using an Aldi version here. Unfortunately most of them are printed with dye sublimation so the packaging printing can't be easily removed. Still - the back of an old knife does the trick and the printing can be scraped off.
Once scraped off, it fits nicely on both my Aldi LED Trekking Torch and one of my various Sipik SK68 AA Torches. The Sipik is a smaller diameter (around 26mm) but the torch clip secures the DIY diffuser nicely so that it can be inverted and hung or used as a candle.
Look how nice it looks on the cheapie Aldi torch - like a little fluorescent tube.