50mm between screw holes. These gasket O Rings seem impossible to find outside of buying a complete unit for $55+. The complete petcock is available on Eblag. Just Google search "Suzuki 50mm vacuum fuel petcock" to find purchase options. I'm including a photo of the correct gasket with measurements. I'm currently contacting sellers if they have the O Ring gasket available for sale. So far, no luck. I suggest you use my measurements when contacting possible sellers. Good luck.