I guess "fractions are applied literally" was a bit cryptic. What I meant is that 1/4 choke = 1/4 * 0.040" = 0.010", and so on. Of course like everything else these have tolerances, and I don't have my charts from various countries at hand. For example, I think (from memory) Spain marks anything from 0.008" to 0.012" with ****. (And of course they use the metric system, so it isn't exact thousandths.) But choke is hardly a hard science anyhow.

Fred