This is a complete set - #4 thru #16 - of vintage Irwin bits for a hand-crank brace, in the original wooden box. Each bit is securely clamped in the box by two spring clips. A bit care manual is included.
These bits are square-shanked. This shape allows the alligator-style chuck jaws of the brace to securely grasp the bit.
A brace and bit is often favored by woodworkers for boring holes in wood where power tools may remove too much material too fast.
Bluwin was the high-end line of bits made by Irwin.