1st Choice Glass Vials, 1/2 Dram, Pack of 12

What are the measurements of this item (in mm)?

are they safe for liquids for travel

What is the weight of each vial alone, without cap and without orifice narrower? The reason I'm asking is that I want to use these to weigh caffeine powder, using a 20 g scale, so the weight of one vial should not be more than 18 g (less than 2/3 oz.)

How's the glass vs heat? Wanna do some small sample mixes