The Rolex SD4000 (left) and Rolex Explorer II (right) are both made of 904L stainless steel exclusively. There are no platinum or gold counterparts to these watches and are positioned in the Rolex line as bona-fide tool watches. The SD4000 ref 116600 and Explorer II ref 216570 keep the classic lines as their older brothers without the boxy re-design found on the updated Submariners and GMTs.

Both made of 904L stainless steel, the SD4000 and Explorer II proportions match their intended use. The larger Explorer II is designed for both daytime and nightime visibility with its 42mm face, larger indicies, and larger hands that hold more Chromalight luminova for longer lasting glowing at night.

The SD4000 is designed for water pressure and subsequently has a smaller, more compact traditional 40mm watch face, traditional 20 mm lug width (1mm narrower than the Exp II), thicker Triplock crown, thicker caseback, and thicker crystal.

Although very similar in weight, the proportions make the watches wear different. The Explorer II lies flatter on the wrist, and the SD4000 thicker caseback and crystal make it ride higher, even though it appears like a smaller, more compact watch.

Weight measured on an inexpensive electronic scale

The 2mm difference in watch face diameters make a discernable difference when reading the watch, yet one watch is not any less easier to read than the other. From this view, the Explorer II cyclops does make the date easier to read, but when read at an angle, the SD4000 wins. A SD4000 with a cyclops lens affixed would make the crystal uber-tall. Despite the prevailing thinking that because of the SD4000's thicker crystal, a cyclops lens would not work because of the optics involved. Despite this prevailing wisdon, others have shown a cyclops glued to a 3mm thick SeaDweller crystal works just fine.

The Cerachrom ceramic bezel found on the SD4000 is easy to read and the bezel rotates as smoothly as the ceramic Submariner and DSSD bezels, and much easier than the original, non-ceramic SeaDweller 16600 bezels.

I did notice that the SD4000 bezel is very easy to grip as the serrations are deep and extend around the edge of the bezel. I also noticed that the bezel *might* extend a tad more off the edge of the case than the DSSD bezel as it is very easy to grip and turn the bezel, or for a long sleeve shirt sleeve to turn the bezel without noticing it.

The difference in proportions continue with the different casebacks and how they sit on the wrist. The SD4000 (left) caseback is slightly smaller in diameter than the Explorer II (right), but the actual portion that touches the wrist is much smaller on the SD4000 because of the room required for the SeaDweller caseback engraving, and the thicker caseback adds increased height.

After wearing the Deep Sea SeaDweller (DSSD), a 17mm high, 44mm wide, 215g behemoth of a dive watch for almost a year, the SD4000 is a sigh of relief. I have a 6 5/8th wrist and the DSSD was a great weekend watch, but my wrist started to feel beat after a few weeks of wearing it. When my wrist felt beat, I would switch to the Explorer II 216570 letting out a sigh of relief. To let my normal watch wrist recover, I would wear the Explorer II on the opposite wrist for a few days.

The DSSD is a fantastic piece of engineering and I would still be wearing it if the watch was not so top heavy and tall. I believe the DSSD would be more comfortable if it were less tall. I had to keep the DSSD pretty tight on the wrist. The much heavier platinum Daytona rides closer to the wrist and thus does not flop around as much.

The SD4000 is a great combination of rugged watch with thicker everything, yet has the relative comfort of the Explorer II. The traditional proportions from the 1967 SeaDweller on a 40mm case keeps the watch compact. I appreciate the thicker caseback raising the watch case higher allowing clearance between the crown and the back of my hand. A 150g watch is much easier on the wrist. If you like to have your watches slide around a bit like with the older hollow-link, tuna-can bracelets found on the originals, both the SD4000 and Explorer II allow for that without beating up the back of your hand. The SD4000's raised caseback and the slightly raised Explorer II caseback matched with the narrower Twinloc crown allow for both watches to be worn slighly loose

The SD4000 watch face is as visible as the Explorer II, but the hands are not. I appreciate the Explorer II's larger hands and as a result, slightly brighter lume because of the increased mass for extra Cerachrom lume. Additionally, the SD 4000 does not have the orange 24 hour hand, larger indicies, and other orange accents that I appreciate on the Explorer II. Ones who might be leaning towards the Explorer II because of the 24 hour hand and tracking a second timezone might be comforted that there are methods (listed here) for 12 hour watches with a rotating bezel to track a second timezone.

On the comfort side, both the SD4000 and Explorer II offer similar wearing experiences. The SD4000 is feels heavier and slightly taller causing a *little* more watch flop, but not anything like the DSSD. The SD4000 looks smaller on the wrist as the Explorer II, but has the same amount of watch presence. For ones who are desk diving or desk exploring, both watches are a coin flip. The Glidelock clasp standard on the SD4000 might sway me to the SD4000, but that feature is counteracted by the larger hands and dial orange accents, and 24-hour hand resident on the Explorer II. The smaller looking SD4000 possesses some very angular features (raised crystal, raised bracelet end links) that make the SD4000 stand out from the GMTs and Submariners. Between the two watches, I would have a hard time selecting just one. Both the SD4000 and Explorer II have features that I use daily. Too bad Rolex does not make a SD4000 Explorer merging all distinguishing features of both watches into one watch. Now there's an idea...

Red Date Disk

It seems that every Rolex that has some color in it increases its value, as well as just looking cool. The Explorer II 216570 has an orange 24-hour hand, and the red Submariners are grail watches to many collectors. I was able to source an all red genuine, still in Rolex parts package date disk for the 3135 movement in my Rolex 116600 which is a spare part for most likely for the 2002 Turn-O-Graph 116264 that possessed an all red date disk.

The concept is not new. Early Rolex DateJusts had a red date wheel, as did the Turn-O-Graphs

Below are some images of the transformation with the help of my local Rolex certified/CW21 watchmaker. These photos were taken with iOS app Hydra on an iPhone 6+. Hydra takes 50 to 60 images per shot, then combines them together for incredibly hi-res photos.

Here it is in the wild. I tried to capture the laser etched crown in the crystal but did not quite catch it. The slight touch of red makes the Rolex 116600 SD4000 perfect. The blur in the image is the second traveling while the image is captured.

A few more recent picts are below taken on my drive to the office.