So I did it again.

I PPAP'ed a pair of 5606-7000 to put the gold-tone chapter ring, dial and movement onto a steel case.

It's not like nobody has ever done that.

I had a steel 5606-7000 that has a broken date jumper and a somewhat shot dial. So I bought a SGP 5606-7000 with a worn case but good dial and movement, then PPAP'ed them together to make one good watch.

But the point here, is about its mainspring.

Look at this bend.

Where the thick bridle of an automatic mainspring ends and begins to wind into the center coil, it's a slight bend inwards and my clumsy finger had bent it too much, causing the mainspring to break.

I wasn't planning to buy an NOS Seiko original mainspring or any Swiss compatible ones, because for one I have a working barrel on the other 5606 and for another, an ETA 2892 mainspring may fit.

So I ordered a bunch of ETA 2892 mainsprings from China and after a few days of anxious wait, the package arrived.

I placed the washer in reverse so the coil direction is correct for 5606, and pushed the spring in, nope, it had to fly out, all the time, every time.

I had no choice but handwinding it into the barrel, this time without any breakage.

But then the arbor won't fit in no matter how hard I tried.

I took the mainspring out of the barrel, put the arbor in, then handwound the spring in the second time. All good now.

I had a used 5606 barrel and it was giving me 180° amplitude at best, whereas a new ETA 2892 mainspring is giving me 243°.

For all out there, I can confidently say now, you can use ETA 2892 mainspring on Seiko 5606.