Maximum 66mm with the clamp. If you drill a hole in the table up to 76mm. So yes ;-) Have a look at page 3 of the manual:
https://media.ergotron.com/reserved...

Exactly as described by Anonymous. Allow me to make one more comment: I have been using the Ergotron LX Dual Stacking Arm for about a year and am very happy with it. It's solid, robust and offers a wide range of options. However, I would like to point out that 2 monitors on top of each other can be very uncomfortable to look at. For me, 2 monitors next to each other are clearly the better choice in terms of workflow and comfort. And if you have the monitors next to each other, I would rather recommend the model without the "high bar".