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ETA watch movements

ETA is the Swatch Group's movement house and the maker of the Swiss workhorse automatics that set the dimensional benchmarks the rest of the industry matches.

Who ETA is

ETA SA is the movement manufacturer of the Swatch Group and the largest maker of mechanical ebauches in Switzerland. Its calibers, above all the 2824-2 and the thinner 2892-A2, are the reference automatics that much of the mid-range Swiss industry is built on.

Because ETA supplied movements across so many brands for so long, its footprints became de facto standards. A case designed around a 2824-2 defines a size that donor movements from other houses aim to match.

The calibers that set the standard

The 11 1/2 ligne 2824-2 is the benchmark date automatic at 25.6 mm by 4.6 mm. The 2892-A2 is the slim version at 3.6 mm, prized as a thin base and a platform for complications. The 2836-2 adds a day to the date, and the Valjoux 7750 is the industry's standard automatic chronograph.

Each of these has its own page here with the exact dimensions and the movements that share its case, so a donor can be checked against the real datasheet figures.

ETA and the donor market

Swatch Group restricted open sales of ETA movements to outside brands over the 2010s, which is a large part of why Sellita and others grew as drop-in alternatives. Many Sellita calibers are dimensionally matched to their ETA counterparts, which is the whole basis of the drop-in donor idea.

The fitment tool exists for exactly this situation: to check, footprint by footprint, which movement actually drops into a case built for an ETA caliber.

Related

Sources: ETA (Wikipedia) · Movement datasheets (as cited on each caliber page)