SPRON, coined from SPRING MICRON, is an SII brand name. SPRON is a
highly elastic Co-Ni based special metal that features superior material characteristics and precise processing accuracy for precision springs . Jointly developed with the Institute for Materials Research at Tohoku University as a spring material for mechanical watches, SPRON has provided high reliability until now.
The SPRON series has high mechanical strength, durability, heat resistance, and superior corrosion resistance. In particular, the characteristics of non-magnetic SPRON 510 are exploited for a wide range of applications from electronics to the medical field, including small precision springs, metal diaphragms, medical materials, and many others.
As for the Spron 510, it is not used in the 7s movement series that are inside most Seiko 5s. The 4r, 6r and higher series movements have the Spron 510. If you want to double check just test the power reserve, watches with the Spron 510 will get greater than 50 hrs. Mid 1996 – 7S26A introduced
Late 2005 – 6R15A introduced, based on the 7S with Etachron regulator and Spron 510 mainspring
Late 2006 – 7S26B introduced with Etachron regulator
The 4R line up (all beat at 21,600bph):
4R15 – 22 jewels, date only, non hacking, non handwinding, Spron 510 mainspring
4R16 – 22 jewels, day date, non hacking, non handwinding, Spron 510 mainspring
4R35 – 24 jewels, date only (4R35 is now on B series, A series has 23 jewels), handwinding, hacking
4R36 – 24 jewels, day date, handwinding, hacking
4R37 – 24 jewels, date only, 24hr sub dial, handwinding, hacking
4R38 – 24 jewels, no date, open heart, handwinding, hacking
4R39 – 24 jewels, no date, open heart, 24hr sub dial, handwinding, hacking
Movement Beat Winding Hands Date Subdial Jewels Power reserve
6R15 21,600 Automatic Hour, minute, seconds Date window None 23 50 hours
6R20 28,800 Automatic Hour, minute, seconds Day and date window Power reserve indicator 29 45 hours
6R21 28,800 Automatic Hour, minute, seconds Sweep day and date subdials Power reserve indicator 29 45 hours
6R24 28,800 Automatic Hour, minute, seconds Retrograde day and date subdials Power reserve indicator 31 45 hours
6R27 28,800 Automatic Hour, minute Sweep date subdial Sweep date, retrograde power reserve indicator 29 45 hours6R1x (2006)6R15, 6R20, 6R21, 6R24
Spron 510 
The precision and power reserve of a mechanical watch depend greatly on the quality of the balance spring and main spring. SEIKO's unique alloy,
SPRON 510, leads the industry by delivering extended power and accuracy.
Spron 510 is already fitted to entry level 4r15/16 movements, giving them 50+ hours power reserve and better accuracy than the older 7s caliber family.
υ.γ
μαλλον η 7ς26 παει για αποσυρση
