Labs often capture honey bees and then need to introduce them to apparatus or transfer them. The plunger helps to gently introduce a bee into apparatus. This design is a simple modification to a snap cap vial. You will need to drill a hole at the end of vial. I suggest creating/printing a jig and inserting vials. I just cut a hole the size of the vial in a block of wood and clamped it to my drill press. 

https://www.amazon.com/dp/B002VA5TXA?ref=fed_asin_title&th=1

SP Bel-Art Snap Cap Styrene Vials; 3 dram (11ml), PE Cap (Pack of 144) (F17575-0003)

            The printing is straightforward. Note that the vial has an interesting characteristic. It tapers slightly so has a narrower inner diameter at its base than at the cap end. This means that the plunger will usually hold firm when fully withdrawn. I had thought about a fancier design with a TPU gasket but it is not needed. Slight adjustments may be necessary and not all vials are identical. I have included all files for mods. After you print out the stem and stick it in through the drilled vial, apply gentle and firm pressure to push in the vial knob. It is a friction fit. No glue needed. 

            When printing out the stems, be aware of sway, which can cause layer shifts at the top of the print. Note that a bit is fine since that bit will not be seen but is inside the knob. I suggest keeping it slow. This is printed with PETG.

This is what it looks like in use.

The snap cap vial lid is designed with airholes for bees (and a central hole through which a pipette tip can be inserted to feed bees). The idea is that this is much easier than manually making holes in the snap caps that come with the vials. However, the vial lid has another purpose. You cannot easily find replacements for the vial lids, which tend to tear. Also, if you want to easily open and close the lids to rapidly capture and release bees, the vial lids that come with the vials do not work well. Students often complain that they are difficult to put on and get off and that they tear. I've tried it and this is a real problem.

The 3D printed vial caps are designed to solve these problems. Note that to adjust the fit, I simply adjust the fillet size of the ring inside the cap. It is remarkable how sensitive it is. In the final design, I went with a 1.62 mm fillet. This surprisingly worked better than a 1.61 or a 1.62 mm fillet with repeated use. Note that this is printed with PETG with a 0.6 mm nozzle. Why a 0.01 mm difference matters is a bit of a mystery to me, but it works. Files are included for you to make your own adjustments.

Finally, these vials are surprisingly difficult to print. You need to do it very slowly. I think that the issue is the small holes. Printing them singly is not a problem, but when you print 100 at a time, errors pop up and you can easily ruin your whole print run. See the 3mf file that I have included for suggested print settings. This has printed flawlessly 99% of the time.

Enjoy!

James C. Nieh

UC San Diego, School of Biological Sciences

Department of Ecology, Behavior, & Evolution.