A drill with a worn margin will produce holes that are which size?

A drill with a worn margin will produce holes that are which size?

• A. Oversize
• B. Undersize
• C. Exact size
• D. Unfinished

Answer: (B)

When the margin of a twist drill wears, the effective diameter of the cutting portion becomes smaller. The margin helps set and maintain the hole size as the drill penetrates the material. With wear, the drill cuts a little more loosely, so the hole ends up smaller than the nominal size. That’s why a drill with a worn margin produces undersize holes. The other options don’t fit because wear typically reduces, not increases, the hole diameter; an exact size would require no wear, and “unfinished” isn’t a hole-size term.

When the margin of a twist drill wears, the effective diameter of the cutting portion becomes smaller. The margin helps set and maintain the hole size as the drill penetrates the material. With wear, the drill cuts a little more loosely, so the hole ends up smaller than the nominal size. That’s why a drill with a worn margin produces undersize holes. The other options don’t fit because wear typically reduces, not increases, the hole diameter; an exact size would require no wear, and “unfinished” isn’t a hole-size term.