My manual says 7mm x 2mm for the .25, I thought that sounded WAYYYYYYYYYYYYYY to big, so I pulled my O-ring and measured. Yep, 6.5mm x 1.5mm. Must have been a misprint. I had already bought a 7mm x 2mm at the local hardware so I compared them. NO WAY would a 7mm x2mm fit in the breach.
Zonk