Watch Almanac
Seiko

Prospex Speedtimer Mechanical

Ref. SPB513

Case diameter
39.5 mm
Manufacturer spec
Lug-to-lug
44.5 mm
Manufacturer spec
Thickness
12 mm
Manufacturer spec
Lug width
20 mm
Manufacturer spec

Retail price $995 (US, Oct 2026)

Ideal fit
Wrist flat: 55.1 mmLug-to-lug: 44.5 mm

How the Prospex Speedtimer Mechanical wears

Its lugs add only 5 mm to the 39.5 mm case, against 7.1 mm typical across the almanac, so it wears smaller than its diameter suggests.

On our fit model it sits best on wrists from 6.25" to 7.5" (15.9–19.1 cm); below 6.25" the lugs start to reach the edge of the wrist.

At 12 mm thick it is thicker than 52% of the 52 other sport 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; 104 other watches here share it, so aftermarket straps are easy to find.

Will the Prospex Speedtimer Mechanical fit your wrist?

With a 44.5 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 mmSnug, lugs near the edge
6.5"51.2 mmIdeal fit
7"55.1 mmIdeal fit
7.5"59.1 mmIdeal fit
8"63 mmWears small

Specifications

Reference
SPB513
Collection
Prospex
Status
In production
Case material
stainless steel (super-hard coating)
Crystal
curved sapphire
Water resistance
200 m
Bezel
steel bezel with 60-minute scale
Dial
cream
Strap / bracelet
stainless steel bracelet, three-fold clasp
Weight
154 g
Style
Sport, Everyday

Movement

Caliber
Seiko 6R55
Type
automatic
Power reserve
72 hours
Jewels
24
Accuracy
+25/-15 s/day

3 other watches use the Seiko 6R55

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 Speedtimer Mechanical.

Sources