Times-whatever on the wood dowel.
If you have a decent magnifier, use that while comparing the thread pitch to either known pitch threads or use a caliper to measure as many threads as possible and do a little math to figure pitch in Teeth per inch or directly, if Metric.
What is the threaded hole on? It can make a difference. Several manufacturers made proprietary thread pitches for their parts. Winchester, for example, used 14 and a half TPI threads on their High and Low wall 1885 actions, confirmed from factory drawings. Several other gun makers did the same, using threads that were not available a the hardware store. Old British Commonwealth products may contain British Associated (BA) threads, or Whitworth form, German stuff can have about anything, as a lot of the machine tools came out of the US too. And in antique stuff, an apprentice would have used his Master's Screw Plate, to make a screw plate for his own use. that plate was used to make his taps, as well as to thread the screws to fit that tapped hole, so it could be danm near anything...
Add to that, that gun makers have often used many finer than normal threads, for which most tap and die sets do not cover, like many of the scope screw threads, which tend to be higher TPI than the basic fine threads in a tap kit.
