You've got some good advice here; nothing beats the right tool for the job, but with calipers, you can get a good idea of what you have there.
Measure the O.D., it will be a metric size; the O.D. will be smaller than the nominal thread size, for instance, if it measures 23.7mm, it's most likely a 24mm thread, be careful though, because there isn't a lot of quality control with these cheap Chinese parts.
Next, if you're careful, you can measure the thread pitch with your calipers also. Just measure the distance between the peaks of the threads, it will probably be a fraction of a millimeter, such as 0.5mm, 0.75mm, or most likely with that host, I'd guess it to be 1.00mm pitch.
Just to repeat, nothing beats having the proper tools.
Good luck! :yh: