How to measure glass joints

I am looking to buy some more glass off American websites but the only joint size they carry is 24/40. The Chinese lab equipment I have is 24/39… do you think I could get away with using 24/40 on my current 24/39 joint

Just figured out the answer. Ignore this post…can’t figure out how to delete


what is the answer?

A little shorter/longer is usually fine with the conical joints in my experience, but diameter should match