I have an assortment of head shells and cartridges for my turntable, including a couple of somewhat expensive ones.
The stylus guards on them are for the most part pretty good, but I still don't want them sitting out in the open collecting dust between uses.
However, I also want them somewhere convenient to get to when I want them.
I looked into cartridge/shell holders such as the very nice triple one that Audio-Technica makes.
However, they are generally made for straight head shells and all of mine are angled.
Also, they tend to be rather expensive for what they actually are.

So, I designed an insert for softball display cases such are commonly available in hobby stores for $12-$30 (depending upon their construction).
Even the most expensive wooden base and glass sided ones are about half the price of a commercial cartridge case.
The exact case I used is a "Studio Decor" from Michael's Crafts in the 4.2"x4.2"x4.2" (10.6cm x 10.6cm x 10.6cm) size.
I like it because it has a center depression that is perfect for storing the level that I use on the turntable and it has plenty of clearance for the lift arms of the head shells.

This design has four risers so that the cartridge shells are parallel with the sides of the cover, and spaced safely away from contacting it.
The risers have rotation key slots for the alignment pins on the head shell connectors.
The risers are also offset slightly so that the angled shells and lift arms become more or less centered along the sides of the cover.
There is a small lip on the base that forms a tray to store miscellaneous items such as my cartridge alignment gauge, spare screws, and so forth.
The lip also serves as a guide for the cover when placing it in the base.

I had considered a double or triple holder for a round glass dome, but finding the right dome and base turned out to be a bit of a challenge (most of them in a large enough diameter are far too tall).
So in the end a cubed softball case worked the best.

This prints very easily with no supports needed and it works great.

Thanks for looking, I hope it works for you as well.