Every reference with a known width takes the same strap size. Your reference is engraved on the case back or between the lugs at 6 o'clock.
20 mm
Verification: Not yet verified
Attachment: spring bars
42.6 to 44.3 mm cases · 2026
Indicative information. Check your watch before buying a strap: whatsmylugwidth.com is not responsible for an incorrect size.
The Seiko Prospex Marinemaster takes a 20 mm strap: all 5 references with a listed width in our database use 20 mm. Check the reference on your case back to be sure.
Seiko Prospex Marinemaster references in our database. Each card says where its width comes from: listed by the maker (linked to the maker's page in the details), two independent sources agree, or listed in our database and not yet verified by us.
Prospex Marinemaster 1968 Heritage Diver's Watch
Lug width: 20 mm
Source: Not yet verified Attachment: Spring barsCase size: 42.6 mmYear: 2026Black dialCase material: Stainless steel, ceramic bezel
Prospex Marinemaster 1968 Heritage JAMSTEC Limited Edition
Lug width: 20 mm
Source: Not yet verified Attachment: Spring barsCase size: 42.6 mmYear: 2026White to blue gradient dialCase material: Stainless steel, ceramic bezel
Prospex Marinemaster
Lug width: 20 mm
Source: Not yet verified Attachment: Spring barsCase size: 44.3 mm
Prospex Marinemaster
Lug width: 20 mm
Source: Not yet verified Attachment: Spring barsCase size: 44.3 mmGreen dialCase material: Stainless steel
Prospex Marinemaster
Lug width: 20 mm
Source: Not yet verified Attachment: Spring barsCase size: 44.3 mm
No reference matches.
The Seiko Prospex Marinemaster takes a 20 mm strap: all 5 references with a listed width in our database use 20 mm. Check the reference on your case back to be sure. These widths come from our database and are not yet verified.
From our database, which lists 5 Seiko Prospex Marinemaster references, 5 of them with a listed width. Each reference card says whether the maker lists the width, two independent sources agree on it, or it is not yet verified.
The gap between the two lugs that hold the strap, in millimetres. A new strap must match it exactly: 20 mm lugs take a 20 mm strap.
Most watches use spring bars, so any strap of the right width fits. Many smartwatches use their own band system instead, such as Apple Watch bands or Garmin QuickFit.