About Counterbores
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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Inch Size High-Speed Steel Counterbores with Built-In Pilot
The built-in pilot maintains alignment in the hole.
Titanium nitride (TiN) coated counterbores are more wear and heat resistant than uncoated counterbores.
For technical drawings and 3-D models, click on a part number.
Dia. | Pilot | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| For Screw Size  | Body | Shank | Dia. | Lg. | Overall Lg. | Number of Flutes | Flute Style | For Use On | Each | |
Uncoated High-Speed Steel | ||||||||||
| No. 8 | 0.272" | 1/4" | 0.164" | 0.250" | 5" | 4 | Spiral | Aluminum, Brass, Bronze, Iron, Plastic, Stainless Steel, Steel | 0000000 | 000000 |
Titanium Nitride (TiN) Coated High-Speed Steel | ||||||||||
| No. 8 | 0.272" | 1/4" | 0.164" | 0.250" | 5" | 4 | Spiral | Aluminum, Brass, Bronze, Iron, Plastic, Stainless Steel, Steel | 00000000 | 00000 |
Oversized High-Speed Steel Counterbores with Built-In Pilot
Use these oversized counterbores when the screw holes in sheets or layers of material are misaligned. The built-in pilot maintains alignment in the hole. The body diameter and pilot diameter account for the 1/32” or 1/64” oversized diameter rating.
Titanium nitride (TiN) coated counterbores are more wear and heat resistant than uncoated counterbores.
For technical drawings and 3-D models, click on a part number.
Dia. | Pilot | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| For Screw Size | Body | Shank | Dia. | Lg. | Overall Lg. | Number of Flutes | Flute Style | For Use On | Each | |
Uncoated High-Speed Steel | ||||||||||
1/64" Oversized | ||||||||||
| No. 8 | 0.288" | 1/4" | 0.18" | 0.250" | 5" | 4 | Spiral | Aluminum, Brass, Bronze, Iron, Plastic, Stainless Steel, Steel | 0000000 | 000000 |
1/32" Oversized | ||||||||||
| No. 8 | 0.303" | 1/4" | 0.195" | 0.250" | 5" | 4 | Spiral | Aluminum, Brass, Bronze, Iron, Plastic, Stainless Steel, Steel | 0000000 | 00000 |
Titanium Nitride (TiN) Coated High-Speed Steel | ||||||||||
1/64" Oversized | ||||||||||
| No. 8 | 0.288" | 1/4" | 0.18" | 0.250" | 5" | 4 | Spiral | Aluminum, Brass, Bronze, Iron, Plastic, Stainless Steel, Steel | 00000000 | 00000 |
1/32" Oversized | ||||||||||
| No. 8 | 0.303" | 1/4" | 0.195" | 0.250" | 5" | 4 | Spiral | Aluminum, Brass, Bronze, Iron, Plastic, Stainless Steel, Steel | 00000000 | 00000 |
Counterbores for High-Profile Rounded-Head Screws
The built-in pilot maintains alignment in the hole.
For technical drawings and 3-D models, click on a part number.
Pilot | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| For Screw Size | Body Dia. | Head Dia. | Lg. | Overall Lg. | Number of Flutes | Flute Style | For Use On | Each | |
Uncoated High-Speed Steel | |||||||||
| No. 8 | 0.285" | 0.163" | 0.120" | 2 3/4" | 2 | Spiral | Aluminum, Brass, Bronze, Iron, Plastic, Stainless Steel, Steel | 0000000 | 000000 |
Inch Size Drill-Point Counterbores
Drill and counterbore holes with enough clearance for socket head screws without changing tools. The longer the counterbore, the thicker the material it can drill.
For technical drawings and 3-D models, click on a part number.
Dia. | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| For Screw Size | Body | Shank | Drill Tip | Overall Lg. | Max. Hole Drilling Dp. | Number of Flutes | For Use On | Each | |
Uncoated High-Speed Steel | |||||||||
| No. 8 | 0.290" | 5/16" | 0.178" | 1 15/32" | 0.281" | 2 | Aluminum, Brass, Bronze, Iron, Plastic, Stainless Steel, Steel | 00000000 | 000000 |
| No. 8 | 0.290" | 3/8" | 0.178" | 2 1/4" | 0.534" | 2 | Aluminum, Brass, Bronze, Iron, Plastic, Stainless Steel, Steel | 000000000 | 00000 |
Oversized Long-Life Counterboring Drill Bits
These counterbores are often used when screw holes in sheets or layers are misaligned. Also known as subland drill bits, they last longer than standard counterboring drill bits because the diameter stays the same after sharpening. They drill and counterbore at the same time. After drilling and counterboring, tap the hole and install your fastener. The diameters account for the 1/32” or 1/64” oversized diameter rating.
For technical drawings and 3-D models, click on a part number.
Dia. | Lg. | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| For Screw Size | Body | Step | Step | Overall | Number of Flutes | Point Angle | For Use On | Each | |
Uncoated High-Speed Steel | |||||||||
1/64" Oversized | |||||||||
| No. 8 | 0.281" | 0.175" | 3/8" | 4 1/4" | 2 | 118° | Aluminum, Brass, Bronze, Iron, Plastic, Stainless Steel, Steel | 00000000 | 000000 |
Long-Life Counterboring Drill Bits
Also known as subland drill bits, these last longer than standard counterboring drill bits because the diameter stays the same after sharpening. They drill and counterbore at the same time. After drilling and counterboring, tap the hole and install your fastener.
For technical drawings and 3-D models, click on a part number.
Dia. | Lg. | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| For Screw Size | Body | Step | Step | Overall | Number of Flutes | Point Angle | For Use On | Each | |
Uncoated High-Speed Steel | |||||||||
| No. 8 | 0.272" | 0.164" | 3/8" | 2 11/16" | 2 | 118° | Aluminum, Brass, Bronze, Iron, Plastic, Stainless Steel, Steel | 00000000 | 000000 |
Counterboring Drill Bits
Often called step drill bits, these drill and counterbore holes at the same time. After drilling and counterboring, tap the hole and install your fastener. The body diameter may decrease after multiple sharpenings.
For technical drawings and 3-D models, click on a part number.
Dia. | Lg. | |||||||
|---|---|---|---|---|---|---|---|---|
| For Screw Size | Body | Step | Step | Overall | Point Angle | For Use On | Each | |
Uncoated High-Speed Steel | ||||||||
| No. 8 | 0.290" | 0.178" | 1/2" | 4 1/4" | 118° | Aluminum, Brass, Bronze, Iron, Plastic, Stainless Steel, Steel | 0000000 | 000000 |