I had the same question! I called a nice guy at Kuchenprofi USA and he measured the funnel for me. No contact info found on Amazon. The opening that goes in the bottle is 1 and 3/8 inches. Hope that's helpful :)
I absolutely agree with Myung Kwon: a funnel description is not complete without the diameter of the stem.
I need to pour powder from a large jar into one with a 1 1/2" mouth. My canning funnel has a stem diameter larger than the mouth of the smaller jar, and all my other funnels are so small - and have such long stems - that the powder keeps clogging them up.
This looks like the perfect solution. But if I'm going to pay this much for a funnel, I need to know for certain that it will fit into the mouth of the jar.