I love changing straps on my watches, but with some pieces in my collection, I hesitate. If you have a watch that is synonymous with its on-bracelet look, you’ll know what I am talking about, and that can be despite its less-than-perfect wearability. So I wondered, can a curved-end rubber strap transform the beefy Marinemaster 300?

For me, the Seiko SLA023 was the final step on my Seiko diver journey, and just like a Tudor Black Bay 54 or Speedmaster, many feel that it looks best on its original bracelet. Most Seiko divers are known for superb quality and finishing with a scarily perfect and soft case shape for their size. But the bracelets come under criticism. Still, it took me two years of hesitation to get a curved-end rubber strap from Crafter Blue.

curved rubber

First impressions and fit

The SLA021/023 are this decade’s Marinemaster 300s, despite the name not being on the dial anymore (and I will fight you about it if necessary). The case is the same and still finished by Grand Seiko, making it seem way too perfect for a diver. It’ll beat a Rolex at twice the price, especially with its new ceramic bezel and fat sapphire crystal. But the bracelet has big links, so despite the micro-adjustments, it is not easy to get a perfect fit. And you’ll always be conscious of its weight and thickness. Make no mistake: this is not a small watch. It’s comfortable, yes, but it’s still beefy. By the way, this is a Crafter Blue strap that I paid full price for, so there is no sponsorship here. The company is known for its Seiko-specific straps, which are available for many models, including the classic SKX.

Out of the guarantee-card-equipped package that included a new set of fat spring bars, the only scary thing was cutting the strap to fit. This means the holes in the clasp remain the only means of adjustment, not counting the ratcheting function of the clasp. The strap, however, is expertly curved and reinforced at the dramatically angled lug end, providing a great, snug fit. The vulcanized rubber has a lovely banana/vanilla scent and does not attract dust like silicone does. So far, so good, and it hugs the wrist with soft confidence. It also makes the deep blue dial and bezel seem even fresher in its blue symbiosis. For me, despite its non-OG Marinemaster color, blue will always be better than black, so sue me.

curved rubber

The specs that change things

I have a medium 17.5cm (7″) wrist, and the main difference in fit, in addition to reduced weight, is the angle at which the strap drops down from the lugs. The lug-to-lug of the MM300 is about 51mm, but it has male-style end links, making it closer to 53–54mm in real life. Despite the flexibility of the bracelet, that is long. The calipers came out to see exactly what changed.

curved rubber

In the shot above, you can see the sharper downward angle of the vulcanized rubber strap, and measured in line with the holes for the spring bars, the span is close to 51mm. That’s almost a 3mm reduction from the bracelet’s end links, which makes a huge difference in comfort. Weight-wise, the strap saves 26 grams, including the same big ratcheting divers clasp carried over. On a slimmer clasp, you’d save more and increase the comfort.

Will the watch stay on the rubber strap?

Don’t get me wrong; I might change it up now and then, but the SLA023 now feels at home on this curved-end rubber strap. Perhaps it looks a bit too modern for some purists, but it just works for me. The only thing I’ve had to get used to was the unseasonable and newfound comfort of the SLA023. It has been a watch that was one of the reasons for seeing my collection in a new and seasonal light, but that might change.

Sure, it’ll never “slip under a cuff” (a phrase I’ve used in too many articles), and the 15.4mm thickness can’t be hidden. But it still feels softer on my wrist and ever-so-slightly less bulky. As I still don’t own a wetsuit, I will probably swap the clasp for a slimmer version. That should make the watch even more wearable. The stronger emphasis on blue is only a big plus, and for me, it is still Seiko Diver’s Watch Numero Uno, despite the modern LX series.

curved rubber

Final notes

I know this is a Seiko legend and deserves a proper clasp, but my love/hate relationship with ratcheting clasps continues. I mean, with a 9–10mm thickness, it’s virtually like wearing a dress watch on the underside of your arm. And if I’m not diving, then what’s the point, right?

I will also add that I have also tried the watch on a delicious cocoa-colored Tropic-style rubber strap. This made the blue pop even more and is a cool budget alternative. Look in our shop for a 20mm version, which might hit the mark. The blue curved-end rubber strap in this story is available in a few colors for US$75 from Crafter Blue.

What about you, Fratelli? Are you sticklers for originality, or are you hesitantly willing to try alternative straps? Let me know about your favorite newfound combos in the comments.