About Counterbores
![](https://www.mcmaster.com/prerenderstable/mvPRE/contents/gfx/small/a2bga60_abbr.png?ver=1276007986)
Counterboring—Enlarge the top of an existing hole to create a cylindrical-shaped opening with a flat bottom that acts as a seat for the head of a screw or wood plug.
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Drill-Bit Counterbores
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Shown with Drill Bit (Sold Separately)
Attach one of these counterbores to a standard jobbers’ or brad-point drill bit (sold separately) to convert it into a counterboring drill bit. Lock the counterbore into position on the drill bit with the two set screws.
Optional collar (not included) controls the cutting depth of your counterbore. It attaches with two set screws.
For technical drawings and 3-D models, click on a part number.
Counterbores | Optional Collars | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
Body Dia. | For Drill Bit Size | Overall Lg. | Number of Flutes | For Use On | Each | OD | Wd. | Each | ||
Uncoated Steel | ||||||||||
5/8" | 1/4" | 1" | 4 | Plastic, Wood | 0000000 | 000000 | 7/8" | 1/4" | 0000000 | 00000 |
5/8" | 3/16" | 1" | 4 | Plastic, Wood | 0000000 | 00000 | 7/8" | 1/4" | 0000000 | 0000 |
3/4" | 1/4" | 1" | 4 | Plastic, Wood | 0000000 | 00000 | 1" | 1/4" | 0000000 | 0000 |
3/4" | 5/16" | 1 1/8" | 4 | Plastic, Wood | 0000000 | 00000 | 1" | 1/4" | 0000000 | 0000 |
7/8" | 3/8" | 1 1/4" | 4 | Plastic, Wood | 0000000 | 00000 | 1 1/8" | 1/4" | 0000000 | 0000 |
1" | 7/16" | 1 3/8" | 4 | Plastic, Wood | 0000000 | 00000 | 1 1/4" | 5/16" | 0000000 | 0000 |
1 1/8" | 1/2" | 1 1/2" | 4 | Plastic, Wood | 0000000 | 00000 | 1 3/8" | 5/16" | 0000000 | 0000 |
1 1/4" | 9/16" | 1 5/8" | 4 | Plastic, Wood | 0000000 | 00000 | 1 1/2" | 3/8" | 0000000 | 0000 |