This is a clock winding key made for an antique clock manufactured 1920. This has an opening of about 3.69mm and is tapered to 3.19mm to fit the shaft correctly.

Printing this is quite simple, just print it the way it orients. With they keyhole up and it prints perfectly. No rafts or supports are needed, which is why I designed it this way.

If you need one with larger holes for different sized clocks, let me know ill be more than happy to accommodate them!