The "approximately" in the product description is correct. I found the 1/4" dowels to be small enough that they fit very loosely in the 1/4" hole, just enough to swing freely without the tight fit you get from a 1/4". -Dowels would expect. The 3/8" size, on the other hand, is too big to fit the 3/8" hole. I do not recommend them for wood assembly projects where you will be drilling the correct 1/4" and 3/8" holes. If you use them for any other purpose, e.g. for an art project, they're fine as long as you don't need exact/standard sizes.