The Basics

The Fortis Monolith Chronograph ref. 638.18.31 features a black dial with over-sized stick indexes, housed in a PVD coated stainless steel case of 42mm. The bracelet is as black as its case.

Brand: Fortis
Family: Cosmonautis
Reference: 638.18.31
Name: Official Cosmonauts Chronograph Monolith
Produced: N/A
Limited: No

Below is a detailed look at Fortis’s model 638.18.31 from Cosmonautis watch family, including the price, case details and movement features.

Fortis Cosmonautis 638.18.31

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The Details

Fortis’s Official Cosmonauts Chronograph Monolith (638.18.31) was originally released in N/A. This watch features a automatic movement beating at a frequency of 28800 bph ( 4 Hz) to provide a 42-hour power reserve when fully wound.

The Case

The stainless steel case measures 42mm in diameter and roughly 15.5mm thick, with 20mm lug width. The round case is paired with a black color dial with stick-shaped hands, and a arabic numerals hour markers and minute track, covered by a sapphire glass. Fortis’s Cosmonautis model 638.18.31 water resistance is not available. This does not mean this watch is not water resistant. A solid caseback is over the back of the watch case.

Material: Stainless steel
Glass: Sapphire
Back: Solid
Shape: Round
Diameter: 42mm
Height: 15.5mm
Lug Width: 20mm
W/R: N/A

Case Diameter

Case Thickness

Lug Width

Water Resistance

The Movement

The Cosmonautis 638.18.31 movement is a powered by caliber 7750 made by ETA. The 25-jewel automatic movement is 30mm in diameter. Its balance wheel oscillates at 28,800 semi-oscillations per hour or 4 Hz. This movement offers a 42-hour power reserve.

Type: Automatic
Brand: ETA
Caliber: 7750
Base: N/A
Display: Analog
Diameter: 30mm
Jewels: 25
Reserve: 42 hours
Frequency: 28800 bph
Time: Hours, Minutes, Small Seconds
Chronograph: Chronograph

The Price

How much does the Fortis’s Cosmonautis 638.18.31 cost? This watch was introduced in N/A and has been in Fortis’s collection for around . This watch is not a limited release. As with most luxury watches, the price of depends on the availability and demand.

CURRENT PRICE: Not Available

For more information, visit Fortis online.


  • Brand: Fortis
  • Model: Official Cosmonauts Chronograph Monolith
  • Reference Number: 638.18.31
  • Limited: No

Case & Dial:

  • Material: Stainless steel
  • Glass: Sapphire
  • Back: Solid
  • Diameter: 42
  • Thickness: 15.5
  • Lug Width: 20
  • Dial Color: Black
  • Indexes: Arabic Numerals and Stick-shaped hands
  • Water Resistance: N/A meters


  • Winding: Automatic
  • Brand: ETA
  • Caliber: 7750
  • Display: Analog
  • Diameter: 30mm
  • Jewels: 25
  • Power Reserve: 42 hours
  • Frequency: 28800 bph
  • Functions: Hours, Minutes, Small Seconds

About Fortis

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