What tapping drill is commonly used for M8 × 1.25?

A 6.8 mm drill is a common starting size for an M8 × 1.25 cutting tap. Confirm the material, required thread engagement and tap manufacturer data before production.

What is the difference between metric coarse and metric fine?

Fine threads use a smaller pitch than the corresponding coarse thread diameter and therefore require a different tapping drill.

Can a cutting-tap drill chart be used for thread-forming taps?

No. Forming taps normally require a larger pre-hole. Use the forming-tap manufacturer’s specified drill size.

What information helps select a tap or cutting tool?

Provide the diameter and pitch, workpiece material, through or blind hole, machine type, existing tool reference and required quantity.

Tapping Guide

Spiral-Point vs Spiral-Flute Taps

The hole type and required chip direction are central to choosing between these two common machine-tap geometries.

Compare Tap Types

Through holes

Spiral-Point Taps

Spiral-point or gun-nose taps generally push chips ahead of the cutting action and through the bottom of an open hole.

Common starting choice for machine tapping through holes
Efficient chip movement in the forward direction
Often robust because flute space is not used to carry chips back
Requires enough clearance beyond the threaded length

Blind holes

Spiral-Flute Taps

Spiral-flute taps generally lift chips back towards the entrance, helping prevent swarf accumulating at the bottom of a blind hole.

Common starting choice for machine tapping blind holes
Helix angle and geometry vary with material and application
Useful where chips must be drawn away from the hole bottom
Hole depth and available chip space remain important

Information Needed for Final Selection

Provide the thread size and tolerance, workpiece material and hardness, through or blind hole, thread depth, pre-hole depth, machine and holder, coolant or lubricant, and expected production volume. Tool geometry, substrate and coating should then be confirmed against the manufacturer’s data.

Common Selection Mistakes

Using a spiral-point tap in a blind hole without enough chip clearance
Choosing geometry without confirming the workpiece material
Using the same cutting data for different tap constructions or coatings
Confusing a cutting-tap pre-hole with a forming-tap pre-hole