Full details below taken from Uncle Straps Website

When I released the various options for the Omega Speedmaster, some of my nephews began to make a slight modification to theirs to wear it on their Seamasters. This was such a popular request that I wanted to let others know about the compatibility.

Compatibility

Designed to fit: 20mm Omega Speedmaster, Seamaster 300m with modification

What’s included

One bracelet, one pair of end-links (without modification), one pair of spring bars.

Specs

• Lug width to Clasp: 20mm / 18mm
• Length (mm) : 185mm (including end-links)
• Min length after adjusted : 120mm
• Clasp : Milled 316L Stainless Steel 18mm Double Flip-Lock Diver Clasp
• Thickness (mm) : 3.8mm
• Net Weight (gram) : 80grams
• Finish: Brushed metal/Polished sides
• Spring bar diameter: 2.5mm
• Lug end style : Standard (Hollow) Curved End
• Adjustment type : 6 removable links– pin type adjustment (all links are removable)
• Material : 316L Stainless Steel, all solid links (hollow end links)

• Wondering if this product will work with your watch? I do my best to outline compatibility details here so you can ensure a good match.

  For bracelets, some of the compatible models listed are submitted from my customers, and therefore I can’t guarantee the fit will be perfect.

  Occasionally these matches require some light modifications to fit correctly. I’ve outlined these steps over on the Bracelet Mods, Tips & Tricks page.