Drill bit set Proline 78040K — metal bits Ø4 mm, length 75 mm, 2 pieces

Proline 78040K drill bit set includes two HSS-Co metal twist drills with a 4 mm diameter and 75 mm overall length. These bits are manufactured by grinding for precise geometry and straightness, and they feature a 135° point angle with chamfering adjustment to enable fast, accurate starts and reduced walking during marking. Made from high-class high-speed steel with 5% cobalt, the bits resist high temperatures and are intended for demanding metalworking tasks on high-alloy steels, titanium, stainless and acid-resistant steels, creep-resisting steels, cast iron and other hard-to-machine materials. The straight shank fits handheld drills and drill presses for general repair and workshop use.

Advantages

The 135° point with chamfering adjustment shortens drilling time by improving centring and reducing the need for pilot holes. Cobalt-alloyed HSS construction increases heat resistance and wear life when cutting hard or abrasive metals. Precision grinding provides consistent diameter, straightness and hole accuracy. The standard straight shank ensures compatibility with common chucks on portable drills and bench machines.

Suitable for

• Drilling holes in stainless, acid-resistant and high-alloy steels
• Working with titanium and creep-resisting steels
• Repair and maintenance on metal sheets, profiles and thin-walled components
• Use in handheld electric drills and drill presses

Key specifications

• Diameter: 4 mm
• Overall length: 75 mm
• Material: high-speed steel with 5% cobalt (HSS-Co)
• Point angle: 135° with chamfering adjustment
• Manufacturing method: fully ground twist-drill geometry
• Shank type: straight shank compatible with standard chucks

How to use

Secure the drill bit in the chuck of a handheld drill or drill press, ensuring correct clamping of the straight shank to avoid slippage. Mark and centre-punch the drilling position to improve initial tracking. Use appropriate cutting fluid or coolant when machining stainless, high-alloy steels or other heat-sensitive materials to prolong bit life and maintain cutting performance. Apply steady feed pressure and moderate speed suitable for the workpiece material; reduce speed for harder alloys and increase coolant flow as needed.

Usage recommendations

For best results, start with a small pilot hole when drilling thick or highly hardened sections, keep sufficient coolant flow, and replace bits that show wear or chipping. Match drill speed and feed to the material: lower RPMs for harder alloys and higher RPMs for softer metals to optimize tool life and hole quality.