I searched and was not able to find a discussion addressing my question. I may not have used the correct search terms so if this topic has been covered just point me to that thread and I'l get to reading. :-) How can I find more information about the size of the glass wand/receptacle on replacement whips. Sometimes the size is listed as 18 mm, sometimes it isn't listed. I see 18 mm is the most common though. But how is that measured? Is that the entire diameter from outer edge of glass to outer edge of glass, or the inside rim? I can't seem to figure out the sizes. The one I own, that I originally purchased with my analog, box vaporizer is cracked. Depending on where I measure--inside rim, middle of glass, outside edge--it appears to be 19 mm, 21 mm, and 24 mm respectively (give or take a mm since I don't have scientific measuring tools, just a mini tape measurer and my old eyes). The one I just bought at a local shop, which looked like the right size but is actually too small, appears to measure 15 mm, 17 mm, and 19 mm respectively. I am sure there must be some standard sizes and if 18 mm is the most common standard then there should be a standard larger and/or smaller, right? I can't really bring the old one with me when I go shopping and I can't tell just from pictures whether online shops have the right one. I'm pretty sure 18 mm is smaller than what I really need. Any information or guidance on how to get more information, so I can make educated buying choices?