This is designed from scratch by me but it I was inspired by 3DiyProject design here https://www.thingiverse.com/thing:4325836

I wanted a smaller auger for planting snowdrop bulbs.

It attaches to a drill using a shelf dowel, same as the original design above. The dowels are used for floating/concealed shelves. Try searching on those words - you can buy them online and in DIY stores. The ones I bought were described as 10x100 - they have an M7 thread. The 100mm is the length of the hex plastic section, the threaded part is about 75mm which is just long enough for the printed auger. It also comes with a wall plug which you don't need for this. You can get longer ones such as 10x145 which have a longer plastic section - that should work. You can also get ones with a larger diameter hex section, which may be too big to fit in the drill chuck.

I printed without supports in PETG - it may work in PLA, but for this I prefer PETG for extra strength. I think I used about 5 perimeter walls for strength, possibly more.

The moulded hex section on the dowel has a small flange where it meets the thread - you'll need to trim that with a hacksaw so it fits in the end of the auger. Then just fit the serrated nut on the end and tighten quite tight. I bought some M7 nyloc locking nuts but the supplied nut worked fine.

The auger works very well. I planted loads of bulbs really quickly.

Note: Before I found the correct shelf dowels I tried printing some hex shells and gluing them to a length of threaded rod to make a 3d printed version of the shelf dowel. It broke very quickly, so it's worth the effort to find the right shelf dowel. The hard plastic and the way it's moulded to the metal thread makes for a really good tool.