One dozen cheap clinical mercury thermometers in a 5"x2"x2" box.

4.5" long. They are designed so that the full range of the 2-inch-long graduated scale is from 96 to 106 degrees, so these are not the sort of thermometers you would use to tell the temperature of a room, they are designed specifically for measuring the body temperature of higher mammals. They come sterile in a screw-top plastic tube.

They are single-use thermometers. They retain the highest temperature they have ever recorded. If warmed to a temperature of 101 degrees, it will say 101 degrees. If it cools down to room temperature, it will still say 101 degrees. This has a disadvantage but an advantage as well. The disadvantage is that you can't reuse them of course. The advantage is that you are guaranteed to get an accurate reading. If you see a temperature of 100.3, you will never have to worry about whether the actual temperature was 100.5 or 100.7 or 100.8 and it just cooled down before you read it, or maybe it shifted around. If you see 100.3, you will know that was the highest temperature it was exposed to and you can take your time reading it. And at this price, who cares if they aren't reusable.