Watch Almanac
Seiko

Prospex Marinemaster 1968 Heritage Diver's 300m

Ref. SLA077

Case diameter
42.6 mm
Manufacturer spec
Lug-to-lug
49.3 mm
Manufacturer spec
Thickness
13.4 mm
Manufacturer spec
Lug width
20 mm
Manufacturer spec

Retail price $2,900 (US, Oct 2026)

Ideal fit
Wrist flat: 55.1 mmLug-to-lug: 49.3 mm

How the Prospex Marinemaster 1968 Heritage Diver's 300m wears

Its lugs add 6.7 mm to the 42.6 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 7" to 8.25" (17.8–21.0 cm); below 7" the lugs start to reach the edge of the wrist.

At 13.4 mm thick it is thicker than 67% of the 124 other dive watches we've measured, so expect it to sit tall on the wrist.

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 Marinemaster 1968 Heritage Diver's 300m fit your wrist?

With a 49.3 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
SLA077
Collection
Prospex
Status
In production
Case material
stainless steel (ceramic bezel display)
Crystal
dual-curved sapphire (inner AR coating)
Water resistance
300 m
Bezel
unidirectional diver's bezel
Dial
white
Strap / bracelet
stainless steel bracelet, three-fold clasp with secure lock, push button release and extender
Weight
196 g
Style
Dive, Sport

Movement

Caliber
Seiko 8L35
Type
automatic
Power reserve
50 hours
Frequency
28,800 vph (4 Hz)
Jewels
26
Accuracy
+15/-10 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 Marinemaster 1968 Heritage Diver's 300m.

Sources