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|[[Seiko 6R15|6R1x]]||2006||6R15, 6R20, 6R21, 6R24||Spron 510||Yes |[[Seiko 4R15|4R1x]]||2008||4R15, 4R16||Spron 510||No ...

...the 4R15/16 have a long 50 hour [[power reserve]] thanks to an advanced [[Spron]] 510 [[mainspring]]. This is shared with the 6R15 as well. :[[Spron]] 510 mainspring ...

...ical movement. This movement boasted a 72 hour power reserve thanks to a [[Spron]] 510 mainspring among other improvements. It also features a [[power reser ...

...hacking/hand-winding '''[[Seiko 4R35|4R3x series]]''' which also lack the Spron 510 mainspring. These are sold as an upmarket alternative to the '''7S26C'' ...

...plate. The 8R39 is identical in specification to the 8R28 but features a [[Spron]] 610 balance spring and [[Seiko 9S55|9S "Grand Seiko"]] escapement. ...

In [[2006]], Seiko introduced a "3 days" model, which includes a stronger [[Spron]] 510 [[mainspring]]. This would become standard across the range over the ...

...cking mechanism and pinned balance spring for adjustability. Thanks to a [[Spron]] 510 mainspring, the 6R15 boasts 50 hour power reserve, and the faster-bea ...

...pon which it is based) and [[Grand Seiko]] models, including not using a [[Spron]] 510 [[mainspring]]. ...

Seiko uses their own [[SPRON]] alloy for in-house spring production. ...

Seiko uses their own [[SPRON]] alloy for in-house spring production. ...