Sellita · Sellita SW300-1

Sinn U50, IWC Mark XVIII and Hublot Classic Fusion power reserve: inside the Sellita SW300-1

The Sinn U50, IWC's Pilot's Watch Mark XVIII and Portofino Automatic, and the Hublot Classic Fusion all run on the slim Sellita SW300-1 or a close relative. Current movements last up to 56 hours from full, about two and a third days; ones made before 2021 manage about 42.

Updated September 2026 · Based on manufacturer specs, published reviews and watchmaker/owner reports

Watches that use the Sellita SW300-1

The SW300-1 is Sellita's slim automatic, a millimetre thinner than the SW200-1, so it ends up in dressier watches and in tool watches that want to sit low on the wrist. Luxury brands use it more than you might expect, usually under their own calibre names. IWC calls it the 35111, Hublot the HUB1110 and Bell & Ross the BR-CAL.302. The table covers the watches people search for most.

Specs at a glance

History and where it came from

The SW300 is Sellita's version of the ETA 2892-A2, the thin, higher-end ETA automatic that sat under many luxury "in-house" names for decades. Like the SW200 with the 2824, it appeared once the ETA design's patents had expired and Swatch Group started limiting supplies to outside brands. The current SW300-1 revision updated the gear tooth profile, and Sellita built a family on it: the SW330 GMT, the SW305 with a day/night display and the SW360 with small seconds.

The big change came in 2021. Sellita fitted the whole SW300 family with a new barrel and mainspring that raised the reserve from 42 to 56 hours, beating the 2892-A2's roughly 42. Owners on watch forums traced it to a Sellita technical notice from December 2020. The old and new barrels are interchangeable, which matters for servicing. Brands didn't all update their spec sheets at the same pace, so an IWC or Hublot page may still say 42 hours.

Accuracy in the real world

Sellita grades the SW300-1 the same way as the SW200-1, and brands at this level, Sinn, IWC and Hublot, don't use the cheapest grade. IWC adjusts and finishes its 35111 to its own standard. Owner reports for the Sinn U50 are good, with long-term rates of a few seconds a day fast often mentioned. Some owners feel their SW300-1s run a little steadier than their SW200-1s, but that's anecdote, not a measured difference.

Like other 4 Hz Sellitas, it has a conventional regulator, so any watchmaker can bring the rate in quickly without a full service.

Reliability and servicing

The SW300-1 has a clean record. It doesn't share the SW200-1's reputation for ratchet wheel trouble, and watchmakers see the 2892 layout as one of the best-behaved automatics ever made. Service intervals of four to five years are typical. Parts are widely available, and a replacement movement is easy to source, which is why a Sinn or a microbrand watch with one is so easy to keep going.

Branded versions are a slightly different story. IWC and Hublot usually want the watch back through their own service centres, and their date modules and finishing mean an independent may not have every part. The base movement is still the same, so a competent independent can usually handle the basics.

Quirks worth knowing

• Which reserve do you have? Movements made before 2021 have the 42-hour barrel. Unless the brand says so, you can't tell from outside. A full wind and a stopwatch will tell you.
• Hublot's date. The HUB1110's date window sits further out than a standard SW300-1's because of Hublot's own module. It's a Hublot service item.
• Slim means lighter winding. The rotor is light, so a slow desk day adds little charge. That's more noticeable in a dress watch like the Portofino.
• Date danger zone. Don't use the quickset date late in the evening. Here's why.

How it compares

• ETA 2892-A2: the original. Same size and beat; the SW300-1's 56-hour barrel now gives it the longer reserve.
• Sellita SW200-1: the cheaper, thicker workhorse with about 38 hours. The SW300-1 is the better movement if you can choose.
• Sellita SW330-2: the SW300 with a GMT hand added and the same 56-hour barrel.
• Powermatic 80: 80 hours at 3 Hz, but only in Swatch Group watches.
• Miyota 9015: the Japanese slim 4 Hz option; about 42 hours and a rougher-feeling rotor.

Living with the 56-hour reserve

With the newer barrel, the SW300-1 is on the right side of the weekend line. Take a current Sinn U50 off at 6pm on Friday and, from a full wind, it's still running around 2am on Sunday, so it only stops if the weekend runs long. An IWC Mark XVIII or Hublot Classic Fusion rated at 42 hours is a different case. It stops around lunchtime on Saturday, so you'll be setting it again after any weekend away.

Either way, the number assumes a full spring, and a slim, light rotor doesn't fill it quickly. Watch Winder counts down the reserve for each watch you own and reminds you before it stops. Enter 42 hours if you know yours is an older movement. To check a particular weekend, try the "Will my watch stop?" calculator.

Verdict

The SW300-1 is the better of Sellita's two mainstream automatics: thinner, well behaved and, since 2021, good for 56 hours. It's why a Sinn U50 wears so well and why IWC and Hublot were happy to put their names on it. The only real trap is the reserve. Older and some branded versions are 42-hour movements, so check before you rely on it lasting the weekend.

FAQ

How long does a Sinn U50 run off the wrist?

A U50 with a pre-2021 SW300-1 runs about 42 hours from full. Newer SW300-1 movements with Sellita's updated barrel are rated at 56 hours.

What movement is in the IWC Pilot's Watch Mark XVIII?

IWC calibre 35111, which is based on the Sellita SW300-1 and finished and adjusted by IWC. IWC rates it at 42 hours.

What is the power reserve of the Hublot Classic Fusion?

The automatic Classic Fusion uses the HUB1110, based on the Sellita SW300-1, and Hublot quotes about 42 hours.

Does the IWC Portofino Automatic hack?

Yes. The calibre 35111 in the Portofino Automatic stops the seconds hand when you pull the crown to set the time, and it can be wound by hand.

Is the Sellita SW300-1 a copy of the ETA 2892-A2?

It follows the same layout, size and beat, with Sellita's own revisions, including 25 jewels and, since 2021, a longer-running 56-hour barrel.

How do I know if my SW300-1 has 42 or 56 hours?

Movements made from 2021 have the 56-hour barrel. For an older watch, ask the brand or time it from a full wind until it stops.

Sources

• Caliber Corner: Sellita Caliber SW300-1
• Monochrome: Diving with the Sinn U50
• Monochrome: Hublot Classic Fusion Original hands-on
• Grail Watch Reference: SW300-1 and its branded versions
• Wren: Sellita SW300-1 vs ETA 2892

Keeping it running

• On an average day an automatic gains roughly 4 hours of reserve per hour on the wrist, so about 14 hours of wear fills the Sellita SW300-1. Desk days charge more slowly.
• Most automatics can also be wound by the crown. If yours has stopped, a few dozen turns gets it going before you put it on.
• Off the wrist it stops about 56 hours after it was last full. Stopped sooner?
• On a watch winder, start at about 650 turns per day, both directions. Winder settings for every movement.
• If it does stop, don't set the date between 9pm and 3am. Check if it's safe.

All Sellita movements

Never let it stop

Watch Winder counts down the reserve of every watch you own and reminds you before one stops. It already knows the Sellita SW300-1: type your watch's name and the reserve fills itself in.

Manufacturer's published figure. Real reserve varies with the watch's age and service; check your manual.