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Fillister 8-40 Sight Screw Counterbore
Our editorial team reviews specifications, product data, and field-use information to keep pages accurate.
$16.99
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SKU: 080671841
Overview
Designed for sight-screw work, this counterbore is intended for use with popular sight base screws and is made to Brownells’ exact specification for most sight base applications. It features a 90-degree shoulder and a pilot designed to guide the cut, with dimensions provided for precise setup. The tool is suited to shop use where controlled, repeatable counterboring is needed for sight installations and related gunsmithing tasks.
Why Hunters Choose the Brownells
Made Exact
Specifications for most sight base
High-speed Design
Suited for sight screw counterbore
Sized Popular
8-40 sight screws
Includes Clear
Pilot and body dimensions for
90-degree Shoulder
For precise counterbore geometry
Key Features
- High-speed counterbore for popular sight screws
- Made to Brownells' exact specification for most sight base screws
- Overall size: 2A 1/2 inches (6.3mm)
- Body diameter: .250 inches (6.3mm)
- Pilot diameter: .165 inches (4.2mm)
- Pilot length: 1/8 inch (3.2mm)
- 90-degree shoulder design; use Drill No. 19 for pilot hole
Best Used For
- For gunsmiths fitting popular sight base screws with a precise counterbore setup.
- For hunters maintaining rifles that use 8-40 sight screws and standard sight bases.
- For shop work requiring a 90-degree shoulder and pilot-guided drilling.
- For users needing a tool matched to Brownells' exact specification for most sight base screws.
Specifications
| Body Diameter | .250 in (6.3 mm) |
|---|---|
| Overall Length | 2.5 in (6.3 mm) |
| Pilot Diameter | .165 in (4.2 mm) |
| Pilot Length | 1/8 in (3.2 mm) |
| Recommended Drill Size | No. 19 |
| Shoulder Angle | 90 degrees |
Pros
- Made to exact specifications for most sight base screws
- High-speed design suited for sight screw counterbore work
- Sized for popular 8-40 sight screws
- Includes clear pilot and body dimensions for planning
- 90-degree shoulder for precise counterbore geometry
- Uses Drill No. 19 for the pilot hole
Considerations & Trade-offs
- Designed for 8-40 sight screws, so it is not a general-purpose counterbore for larger or smaller fastener sizes.
- Requires a drilled pilot hole; the listed setup calls for Drill No. 19, so it is a step beyond a simple hand tool.
- The 90° shoulder and fixed dimensions make it suited to the specified application, but that also limits flexibility for nonstandard sight base screws.
- The short 1/8 in. pilot length may be a consideration on deeper or unusually thick workpieces.
Suggested Comparisons
- Sight screw counterbores
- Sight screw installation tools
- Gun-smithing drill bits
- Firearm sight base hardware
Suggested Accessories
- Drill bits
- Gun vise
- Sight installation tools
- Bench block
Frequently Asked Questions
What is this Fillister 8-40 Sight Screw Counterbore used for?
It is a counterbore for popular sight screws, made to Brownells’ exact specification for most sight base screws.
What dimensions are listed for this tool?
The listed dimensions are overall 2A 1/2 in. (6.3 mm), body diameter .250 in. (6.3 mm), pilot diameter .165 in. (4.2 mm), pilot length 1/8 in. (3.2 mm), with a 90-degree shoulder.
What drill bit should be used for the pilot hole?
The product information specifies Drill No. 19 for the pilot hole.
Is this tool intended for a specific sight screw type?
The description says it is for popular sight screws and most sight base screws, but it does not list every compatible screw type beyond that.
Who makes this counterbore?
The manufacturer listed is Brownells.