Exactly, 3/8" = 24 ring. Other popular cigars sizes just off the bat are listed below, as I prepare to fly into the shower. Also, remember that in the case of a figurado, the type of cigar that looks like a pregnant whale, the ring gauge should be measured at both its narrowest and widest points. You will often search a web site and see a certain cigar listed as 5x44/52 or even 6x40/56/48, which means that at the cap the cigar was a 40 ring, then whaled out to a 56 ring at the middle and tapered again, but only slightly to a 48 at the foot.
32 ring = 1/2"
40 ring = 5/8"
48 ring = 3/4"
50 ring = 50/64" or reduced to 25/32"
56 ring = 7/8"
70 ring = 1 3/32"