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.

Thread Production Guide

Cutting Taps vs Thread-Forming Taps

Cutting taps remove material to create the thread. Forming taps displace suitable ductile material without producing chips.

Compare Methods

Chip-producing process

Cutting Taps

Cutting edges remove material and create chips. Flute and chamfer design must suit the material, hole type and chip direction.

Available for a wide range of materials and thread forms
Pre-hole commonly starts near nominal diameter minus pitch for metric threads
Chip control is a central selection factor
Through and blind holes often use different flute geometries

Chipless process

Thread-Forming Taps

Forming taps reshape ductile workpiece material into the thread profile rather than cutting it away.

No swarf is produced during thread formation
Requires suitable ductile material and controlled lubrication
Normally needs a larger and more tightly controlled pre-hole
Torque, machine capability and thread limits must be checked

Do Not Use a Cutting-Tap Chart for Forming Taps

A forming tap needs a different pre-hole because material is displaced into the thread profile. Use the exact tool manufacturer’s drill recommendation for the workpiece material and required thread engagement.

What to Send with an Enquiry

Include the complete thread designation and tolerance, workpiece alloy and hardness, hole type and depth, current pre-hole, machine and holder, lubricant or coolant, current tap reference and required quantity.