The D20's head is protected by a smooth stainless steel bezel which provides adequate protection from drops and impact to the head. Below the bezel sits a double-coated glass lens which looks clearer than regular glass and provides improved light transmission out the front. The exterior of the head is smoothly finished with two series of cooling fins machined on it, though I did notice that they look a little different. While the fins towards around the middle area are cut at sharp right angles, the ones towards the rear are beveled. This makes them look inconsistent somewhat, but not very obviously so. Threads on the head are cleanly cut and anodized. Part of the electronic's PCB can be seen from the rear, the "+" contact is raised and provides a good contact surface.
The body is made up of just the battery tube with no separate tail cap. Inside the battery tube is a additional metal tube in which the battery sits. This tube acts like a piston. It simply slots into the battery tube with its rear sticking out the tail end of the battery tube. A red rubber o-ring sits towards the rear end of this piston which provides resistance to the piston mechanism as well as water resistance. The D20 has an IPX-8 rating, to the depth of which stated by the manufacturer. Incidentally, I could not find any stated depth rating on the NiteCore web site. The interior of the tube has a spring on at the "-" end for the battery contact which ensure there will be no battery rattle, and is also nickel coated which gives it a nicer looking finish. This is a unique switching mechanism for a flashlight which is supposed to provide improved power transmission and durability. However there was one thing I didn't like about it. I find that it provides very poor tactile feedback when depressing the switch. Adding to this, the switch also has short travel. Both these issues results in the poor tactile feedback of the switching mechanism. I found the the switching required more pressure than the earlier single-cell PD models. Thankfully, the Smart PD system also allows the light to be activated via twist action, however by using this twist switch mechanism, you loose the ability to switch or select output levels. The threads on the battery tube is just as nicely cut as those on the head and fit very smoothly together with no grinding or cross-threading. A rubber o-ring sits just below the threads on the tail cap which provides resistance for the twist switch action and also waterproofing. Type 3 anodizing throughout the battery tube is consistent and smooth, the dark gray color matches that on the head very well. Almost the entire outer surface of the battery tube is covered in diamond-textured knurling matching that of the head as well giving the D20 an overall consistent design. There are raised segments towards the rear which help with holding the D20 on a cigar-style grip. Right at the end are are holes which allows for lanyard and key chain attachments and also a removable clip. The switch sits slightly recessed thus allowing the light to tail stand on flat surfaces without problem.
Information: The D20 is capable of 3 levels of output, a fixed 1% (3-5 lumens) and 100% (130 lumens), and a customizable level. It functions exactly the same as the earlier D10/EX10 models. The custom level is what I would call a temporary setting as it will be lost once you switch to either the preset 1% (2 lumens) or 100% (180 lumens) levels. Operating modes has been very well described and explained in the following video. I noticed that the ramping sequence doesn't seem linear to human eyes. It ramps quickly from the minimum level and dimmer levels and less obvious at the brighter levels. This quick ramping speed could make it harder to select the dimmer levels.
The beam profile from my sample provides a medium sized hotspot which has a slight dark circle around it. Overall beam color is very close to perfect white, leaning slightly to the cool side. The spill beam provided provides adequate illumination for peripheral vision. Regulation is very good with 2x AA cells providing a good amount of output as well.
Conclusions: The Good - Machining, fit and finish is excellent. Simple and practical body design. Simple interface for custom brightness setting. Good output intensity and regulation. The Bad - Poor tactile feedback and short travel from the piston drive switching mechanism. The Relative - Almost perfectly white tint, leaning slightly to the cool side. Is able to function as both a push button with momentary function, and twist activated switching mechanism. Is able to tail stand.