This is a mixing paddle for drywall compound. The idea is borrowed from a commercial product (Wal-board tools).
I used PLA plus, printed without support.
For the shaft use 5/16" all-thread (threaded rod) secured using 4 nuts. Use at least 12-14" length of all-thread, which is enough to mix the top half of a 5 gallon bucket. When that is used up, the bottom half of the bucket can be mixed.
Best to use with a corded drill so you don't burn out your cordless drill.
For the drill chuck to grab onto the all-thread, use a grinder or Dremel to shape the last one inch into a square or triangle.