Aeration stone barb actual size?

[ndinh]

I'm buying a SS tube from mcmasters to use as a wand because I already have a stone with the 1/4" barb and didn't want to buy another aeration setup. I'm looking at ID for tubes and they have one that's 0.257" which will fit perfectly if the stone's barb is exactly 0.25" (1/4"). Since I don't have a digital caliper handy, does anyone know the exact OD of the stone's barb? Thx alot!