Watch Almanac
Seiko

Prospex 1968 Heritage Diver's GMT

Ref. SPB381

Case diameter
42 mm
Manufacturer spec
Lug-to-lug
48.6 mm
Manufacturer spec
Thickness
12.9 mm
Manufacturer spec
Lug width
20 mm
Manufacturer spec

Retail price $1,500 (US, Oct 2026)

Ideal fit
Wrist flat: 55.1 mmLug-to-lug: 48.6 mm

How the Prospex 1968 Heritage Diver's GMT wears

Its lugs add 6.6 mm to the 42 mm case, close to the 7 mm typical across the almanac, so its diameter is a fair guide to how it wears.

On our fit model it sits best on wrists from 6.75" to 8" (17.1–20.3 cm); below 6.75" the lugs start to reach the edge of the wrist.

At 12.9 mm thick it is slimmer than 52% of the 124 other dive watches we've measured, so it slides under a cuff more easily than most.

Its 20 mm lug width is one of the most common strap sizes; 156 other watches here share it, so aftermarket straps are easy to find.

Will the Prospex 1968 Heritage Diver's GMT fit your wrist?

With a 48.6 mm lug-to-lug, here is how it wears across common wrist sizes. We estimate the flat top of each wrist from its circumference; measure yours for a closer answer in the fit finder.

WristFlat width (est.)Fit
6"47.2 mmLugs overhang
6.5"51.2 mmSnug, lugs near the edge
7"55.1 mmIdeal fit
7.5"59.1 mmIdeal fit
8"63 mmIdeal fit

Specifications

Reference
SPB381
Collection
Prospex
Status
In production
Case material
stainless steel (ceramic bezel display)
Crystal
sapphire (inner AR coating)
Water resistance
200 m
Bezel
unidirectional diver's bezel
Dial
green
Strap / bracelet
stainless steel bracelet, three-fold clasp with secure lock, push button release and extender
Weight
176 g
Style
Dive, GMT

Movement

Caliber
Seiko 6R54
Type
automatic
Power reserve
72 hours
Jewels
24
Accuracy
+25/-15 s/day

Takes 20 mm straps. See other 20 mm watches and straps.

More Prospex references

Watches that wear the same size

Other watches within 1.5 mm of its lug-to-lug.

Same 20 mm lug width

All 20 mm watches

These take the same straps as the Prospex 1968 Heritage Diver's GMT.

Sources