^ PT18 uses an 18650 cell.
Maybe you meant PT16?
Illumination Supply has V.3
You can see 18350 included in the PT16 specs.
All the first (V.1) PTs had the horrible CooYoo/Blackwater SR71 UI.
Illum. helped them change to V2, still missing a Yobai mode.
V.3 is PT16 only, refering to the longer, wider tube.
I have one, believe me the combo is great, even better after an emitter swap.
The PT16 takes 1 18350 or 16340
The PT18 takes 2 x 18350 or 1 18650
All small PTs (10,14,16,18) will accept each other’s heads, they all go to 8.4 volts, and seem to use the same driver, along with the CooYoo and Blackwater SR71, also made by the parent company Altun.
OK, that’s better, but the OP is looking for the smallest 18350 light, so it’s unlikely that he’s interested in something like PT18 that requires multiple 18350 cells.
This is what you wrote earlier:
And that’s not correct. What you’ve described here is PT16, not PT18.
That’s all I was saying. 
Carry on…
BTW, the PT16 is really nice, actually, apart from the price. I just wish it had a clip.
A clip….?
Interesting you should mention….
finally found one.
The Nitecore MH10 works well, $5.95 at the Nitecore store.
an added benefit of the clip …
It makes it a LOT easier to find the switch
Thanks. This does not look very secure.
It is almost too tight.
The spring tension makes it tilt a bit in the photo.
I’m thinking that the reason for the lack of truly “small” 18350 lights is:
If a manufacturer wants to build a small light that has minimum size and weight as a design goal, then they are incredibly likely to use the smaller and more common CR123/16340 battery format. The 18350 battery being close to the same size but slightly bigger, gets ignored. 
Just stumbled across Nitecore EC11 and added it to the list.
Nice find.
The clip looks reversible, although it would stick out if placed the opposite way.
Surprised it only lasts 45 min on 300 lm mode. Hopefully it would last longer when using the Aspire cell.
You can also add the Sunwayman C13R and the Sunwayman T16R!
Not my favourites in terms of functioning, but the both take 18350s!
EDIT : Another one Jetbeam/Niteye EC-R16 
Can you personally confirm the Sunwayman T16R takes 18350? I cannot find any documentation that says so, everything I see says 1x16340/CR123. If so, it is pretty small. Unfortunately 380Lm is not real competitive with most others in the class.
According to this post from Sunwayman, it does support 18350:
I’ve seen it here
I don’t have any 18350 flashlights myself, but just curious if 16340 and 18350 cells are similar or perhaps identical? I can’t help but noticed there are several posts indicating some flashlights will take 16340 or 18350 cells?
Close but not the same, 16mm vs 18mm, 340mm vs 350mm. Most 16340 will not take a 18350 but some will.
Some 16340s are longer than the 18350, though! I received a Wuben 16340, protected, that is longer than the Aspire 18350 unprotected.
It is not larger,though!
18350 is fatter and weighs 3 grams more than 16340
18350 won’t fit my 16340 Olight S Mini:
the 18350 is not protected, it fits the PT16. A protected 18350 does not fit, too long. There is no built in low voltage protection in the PT16. I consider Protection built into the cell important if the light has no built in Low Voltage Protection and is not user monitored for Low Voltage. There is no Low Voltage indicator built into the PT16.
The transparent carrier fits only 16340/CR123
the black battery carrier fits both 16340 and 18350 (it is 1/2” shorter and narrower than a film cannister).
The PT16 has built in USB charging and will charge either 16340 or 18350, but don’t make the mistake of trying to charge a non rechargeable CR123.
I really like the new USB chargeable 16340 Protected cells sold by Olight, Fenix, and Klarus (all from the same factory, just different labels)
fwiw, the PT18 uses 18650, the heads are interchangeable with the PT16. The 18650 PT18 is also compatible with two 18350.
beamshot, the v11r is modified to 3000k 219c 90+CRI, the PT18 is modified to 4000k 219b 90+CRI, the PT16 is shown with stock 6000k XP-G2 70CRI
Any new players in this segment since last year?
I recently purchased a Armytek Partner C1 V2 that was on sale for $17.00, (though shipping was $10.00), that takes both 16340 AND 18350 cells. It’s just under 3” long and a tad over 3/4” wide. It’s a neat little light.
congrats, steal of a price
When I compare size I also like to focus on Weight
Armytek Partner C1 specified weight empty is 57 grams
there is also a Niteye Eye 10, spec 48 grams w clip
left to right
Ti S Mini 29 grams wout clip, 32 grams w clip, PT16 does not weigh 40 grams, it actually weighs 52 grams, or 57 grams with the new pocket clip, RRT-01 actual weight is 48 grams empty, w clip
The PT-16 is 2.75” tall and 1 1/8 wide, so shorter, lighter (w out clip), but fatter, than the Armytek
The Sunwayman T16R is the same weight as the Ti S Mini, and almost as short, but fatter.