Accepted tapping practices for 7/16 inch spouts with no vacuum called for tap holes to be drilled 2-2.5 inches deep. Later practices for 5/16 inch spouts under vacuum, call for drilling the tree to a depth of 1.5 inches. The reason for the reduction in depth, was to reduce the occurrence of drilling into dead wood, especially on trees with a long history of tapping. This can lead to reduced sap yield. When the 2018 season left us with an unusually low sap yield, the question arose: does tap depth matter when the system is under vacuum?
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