Spec-wise, the watches are identical to the SPB143 and the SPB153. They’re powered by the 6R35, a caliber that’s broadly used across Seiko’s entire range and has settled in as a tried and true mid-tier movement. Both feature a stainless case, the SPB239 at 40.5mm and the SPB237 at 42.7mm (they’re both 13.2mm thick), with a water resistance rating of 200m. Everything you’d expect, like a screw-down crown and caseback, and a sapphire crystal, are present.