Drill Bits / #25 Diameter
10-24 Tap Drill Size is a #25 Drill Bit
The correct tap drill size for a 10-24 UNC thread is a #25 drill bit, which has a diameter of 0.1495 inches (3.80 mm).
For a 10-24 UNC thread, a #25 drill bit is used to produce a hole diameter of 0.1495 inches (3.80 mm). This size is commonly specified to achieve consistent thread formation without excessive tapping load.
Selecting the Proper Drill Before Tapping
The drilled hole establishes the foundation for the finished thread. Using a #25 drill for a 10-24 tap ensures the tap engages correctly and cuts clean threads in machine screw and general fastening applications. Deviating from this size can affect both cutting performance and final thread quality.
Hole Size and Thread Engagement
A hole drilled with a #25 bit typically results in approximately 70–75% thread engagement, which is standard for most production work. This range provides adequate holding strength while avoiding unnecessary torque. Increasing engagement raises tapping forces, while reducing it can compromise thread integrity.
Why Drill Size Accuracy Matters in Production
Correct drill sizing is critical for maintaining tool life and process consistency. In both CNC and manual operations, using the specified 0.1495" (3.80 mm) drill size for a 10-24 tap helps prevent tap breakage, reduces variation in thread fit, and supports repeatable results across batches.
Additional Tap Drill Size References
For other thread sizes and complete drill charts, refer to the resources below.
