KW - you are correct. The holes are 4". I used a 1 x 8 which for 6 wine bottles is sturdy enough. If you make the racks longer (more than 8 bottles across) you may want to go with a wider board to hold the weight of full wine bottles. I drew a center line on the board and marked the center of the 4" holes. The circles have a 1/2" space between them. When I drew the center line, I also drew a line a 1/2" on both sides of the center line. After the holes are cut out, I then ripped down both lines next to the center line. Makes the rack look better than a perfect half circle. Naturally after you rip the lines you end up with 2 racks. My wine rack is 30" across, so with the 3/4" thick sides, my racks are 28 1/2" long. Make sure you have at least 1" on the ends of the racks to allow for enough wood to handle the screws to hold them to the sides.
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