Parametric Plug / Cap / Stopper

I designed this specifically for [a cheap set of hex drivers with small, hollow handles](https://www.banggood.com/7PCS-BlackBlue-Stainless-Steel-Hex-Screw-Driver-Screwdriver-Kit-Repairing-Hand-Tool-p-1110256.html?rmmds=search&ID=229&p=YL191610202243201704). I carry some of these cheap drivers in my [quadcopter backpack](https://blog.patshead.com/2018/01/thinktank-fpv-helipak-should-i-spend-200-on-a-backpack.html), and putting a plug in the end lets me store appropriate spare screws inside the h