You spent half the morning carefully planing boards to glue into a tabletop—now do the rest of the job right, too! These grooved blocks will hold the bar clamps upright so they won’t ﬂop over when you tighten the boards in the clamps.
To make them, use your table saw to cut a 3/4-in. deep slot midway along the face of a 2×4. You want a snug ﬁt for the bar, so stop and test-ﬁt it in the slot as you widen the slot with additional passes. Now crosscut the slotted 2×4 into 4-in. long blocks, press the bars into the slots, and glue that tabletop without the maddening clamp ﬂops. P.S. Slotted blocks work well to hold round pipe clamps, too, as long as you cut extra-snug slots.