[Jenson71]

Originally Posted by Iowanian

Google search DIY Mason Bee house.

There are a lot of different designs.
the holes should be 5/16
cover with hardware cloth to prevent birds from getting them.

I've seen designs that look like bird houses with the tubes like you have above, small logs just drilled out, or scrap wood glued together and drilled. Some drill from the end of the grain and some from the sides.

https://www.hobbyfarms.com/make-a-mason-bee-house/

Thanks, that looks good. Just one entrace/exit per "nest," at least six inches deep.