Countersinks: what Claude and GPT would buy
Two AI models chose on their own, with no web access. Nobody tested these products: this is what each one says, and how to check it.
Claude and GPT choose the same brand, KEO
In Industrial & Scientific, Claude and GPT choose the same brand in 52 of 107 categories.
Claude Opus 5.5 · October 28, 2026
KEO (brand)
KEO is an established US cutting-tool maker whose countersinks come in the standard included angles, flute styles and HSS, cobalt and carbide grades, so you can match the tool to the fastener and the material.
Not for: Woodworkers who only need a hex-shank countersink with a pilot bit for wood screws in a cordless drill.
GPT 6.1 Sol · November 10, 2026
KEO (brand)
I’d choose KEO for metal countersinking and deburring, selecting the diameter and included angle to match the hole and fastener.
Not for: Buyers needing a specific model recommendation without checking application requirements.
Which one fits you
chatter-free deburring in metal
Weldon (brand)
Weldon's zero-flute, cross-hole countersinks cut smooth, round chamfers in steel and aluminum where fluted countersinks tend to chatter.
Not for: People cutting large countersinks in wood or plastic, where a fluted tool clears chips better.
center holes for lathe work
Chicago-Latrobe (brand)
Chicago-Latrobe's HSS combined drill countersinks (center drills) are a long-standing machine-shop standard for 60° lathe centers.
Not for: Anyone countersinking for flathead screws, since a 60° center hole does not match screw heads.
Check before you buy
Where to find KEO
- Suncoast Precision Tools
- Penn Tool Co.
- Travers Tool Co.
Shops seen in search results on November 6, 2026. A shop missing here may sell it too. Nothing was checked by a person.
Brands that matter
- KEO: Broad US line of countersinks and center drills in HSS, cobalt and carbide.
- Weldon: Known for zero-flute, cross-hole countersinks for metal.
- Chicago-Latrobe: Machine-shop staple for center drills and countersinks.
- Precision Twist Drill: Industrial drills and center drills at shop-grade quality.
- Drill America: Value-tier industrial countersinks and center drills.
- Hertel: Distributor-brand industrial tooling, including countersinks.
What to avoid
- Unbranded multi-flute coated sets used in metal, which chatter and dull quickly.
- Using a 90° metric countersink for 82° inch screws, or the reverse.
- High spindle speeds when countersinking, a main cause of chatter.
Questions
82° or 90°?
Inch (UNC/UNF) flathead screws use 82°. Metric countersunk screws use 90°. Check what fasteners you use.