Introduced in 2008, the Seiko Instruments Inc. (SII) 4R family is a mainstream automatic watch movement used in many Seiko models and offered to third parties by Time Module Inc. (TMI). It is an evolution of the Seiko 7S family of movements, produced since 1996, and is related to the higher-end Seiko 6R family.
There are two branches of the family: The 4R1x movements (4R15, 4R16) came first and have an advanced Spron 510 mainspring but lack hacking and hand-winding. The 4R3x movements (4R35, 4R36, 4R37, 4R38, 4R39, 4R57, 4R71) appeared after 2010 and have a traditional mainspring but add hacking and hand-winding. The 6R family has both improvements.
All movements in the 4R family operate at 21,600 A/h and measure 12 ligne (27.4 mm) in diameter by 5.32 mm in height. Cal. 4R15 and 4R16 have 22 jewels, Cal. 4R35A has 23 jewels, and all other 4R and NH movements have 24 jewels. The NH series movements sold by Time Module Inc. (TMI) are rated as slightly more accurate from the factory, at -20/+40 rather than -35/+45 for the Seiko branded movements, and some differ in the finish, number of jewels, and rated power reserve.
There are only a few complicated members of the family, with a 24 hour subdial (4R37 and 4R39), or date by pointer subdial and power reserve indicator (4R57).
| Traditional Mainspring Hacking/Hand-Winding | Spron 510 Mainspring | |
| Standard | 4R38A NH38A 4R71A (skeleton) NH70A (skeleton) NH71A (skeleton, gilt) | |
| Date | 4R35A 4R35B NH35A | 4R15A 4R15B NH15A |
| Day and Date | 4R36A NH36A | 4R16A 4R16B NH16A |
| Date, 24 Hour Subdial | 4R37A NH37A | |
| 24 Hour Subdial | 4R39A NH39A | |
| Date by Pointer Power Reserve | 4R57A |
