The SRPJ45K1 revives one of Seiko’s more unusual archive pieces — the 1970s “Time Sonar” — in the SKX-shaped case that’s become a modern Seiko 5 Sports staple. The party trick is the translucent blue dial, which lets you watch the day and date discs rotate underneath rather than sitting behind a solid printed dial.

The 42.5mm stainless steel case carries a two-tone unidirectional bezel with a 60-minute countup scale, a push-down crown at 4 o’clock flanked by guards, and a see-through screw-down caseback showing the movement. LumiBrite-treated hands and markers keep it legible at night, and the red-orange central seconds hand adds a distinctive pop against the blue dial.

Inside is Seiko’s in-house 4R36 automatic caliber — hacking, hand-winding capable, 24 jewels, and around 41 hours of power reserve. Water resistance is rated to 100m, and the stainless steel bracelet closes with a three-fold clasp and push-button release.

Key Features
Seiko In-House Cal. 4R36 Automatic – Hacking, hand-winding, ~41hr power reserve
100M Water Resistance – Suitable for swimming and daily wear
Translucent “Time Sonar” Dial – Day/date discs visible through the dial
See-Through Caseback – Movement on display
42.5mm Case, 46mm Lug-to-Lug – Compact-wearing despite the sports-diver silhouette
165g Weight – Substantial but balanced on the wrist
LumiBrite Hands and Markers – Reliable low-light legibility

Why Choose the SRPJ45K1?
✔ Genuinely unusual dial concept, not just another printed sunburst face
✔ Automatic movement with hacking and hand-winding in Seiko’s proven 4R36
✔ SKX-inspired case shape that’s earned a loyal following in its own right
✔ 100m water resistance and a see-through caseback for the price
✔ Red-orange seconds hand adds real character against the blue dial

Shipping, Returns & Warranty

🚚 Free insured shipping on Australian orders of $150 and above
🌏 International shipping available, including New Zealand at a flat AU$22
🛡️ Covered by manufacturer warranty, with 15-day change-of-mind returns — see our Warranty & Authenticity and Shipping & Returns pages