Seiko & Citizen Watch Forum Message Archive

You are correct that a copy of the 6105-8xxx crystal is all that should be needed. I imagine that the crystal company would like a dimensioned line drawing to set up the grinding machine though. Also an on-hand actual case would provide the final quality control check to ensure that the new crystals pass their part of a waterproof/pressure test.

Most modern Seiko watches make their crystal seal on the outside diameter edge against the case (radial pressure). The 6309/6105 make the seal by applying downward pressure via the retaining ring onto a soft rubber gasket. This was a great design as greater water pressure forced the crystal harder onto the gasket.

The 6309 crystal is flat on both sides; the 6105 is concave on the inside giving a slight visual magnifying effect to the dial and hands. Try a 6105 crystal on your 6309 for a quick idea of what a slightly domed synthetic will look like.

Hope this helps.