How about a Square Taper Adapter?

Measuring one of my bits:

Taper is 3/8" on the flat at the widest point, 1-1/4" long and tapers to 7/32" at the narrowest point. I don't think the exact dimensions are critical.

Jack - Perfect! Thank you.

I'll be making some parts shortly and testing.

Much appreciated.

Your goal would be to allow people to use more modern bits in a bit brace? I'm certainly not knowledgeable enough to say, but it doesn't seem to me that most of the bits we would use with electric drills would be well suited to a bit brace. I remember using them as a kid occasionally with my Dad.

You know what could be really handy in a location with no electricity? Those "push drills", or whatever they were called. Before cordless tools, those were awfully handy for drilling pilot holes, and for driving the screws, for that matter.

Yankee screwdriver.

My Dad had a few and loved them. A couple of them were all chrome with special bits that stored in the handle. Small, portable and never need charging. I may have to dig around and find those, even for my own use. But working with no power? Those would really be a blessing.