No flexibility to speak of. Ideally, none at all. Many of us have applied a strip of 1/2″ thick foam insulation tape along the far edge of the base. This provides a nice place to rest the rods, with or without paddles. It also all but eliminates any sound from dropping the handles onto the base.
This next photo shows foam along both the near and far edges. I don’t use the near foam anymore, but the photo shows a pair of stones resting on the foam strip.
The paper was placed to allow the viewer to better see details about the clamping screws more easily.
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