I also found them 1/4" smaller than the listed size. I got about a 15/64, which is close to the 6mm posted by another reviewer. I use dowels to connect furniture and I need them to fit together snugly. I use a dowel setting tool that offers 1/4", 3/8" and 1/2" holes, so switching to a 15/64" bit isn't really an option. The pens themselves appear to be well made and consistent. I also tried getting them wet to see if they would swell to 1/4" but no luck. I chose a different brand.
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