Twist Drill Bits DeWalt DT4939 HSS-E Cobalt 8.5 mm — pack of 10

Set of 10 DeWalt DT4939 HSS-E cobalt twist drill bits, 8.5 mm diameter, supplied as a pack for metalworking and industrial tasks. These high-speed steel (HSS-E) drill bits contain cobalt alloying to increase hardness and heat resistance, making them suitable for drilling hardened steels and other metallic materials. The 8.5 mm size is useful for creating medium-diameter holes in maintenance, fabrication, and workshop operations, and the bits are compatible with standard hand drills and drill presses.

Advantages

The DeWalt DT4939 HSS-E cobalt drill bits offer improved wear resistance and higher red hardness compared with standard HSS bits due to the cobalt content, extending cutting life during prolonged or high-temperature drilling. Their twist geometry provides efficient chip removal and stable centering when drilling through metal. Supplied as a set of ten, the pack ensures consistent replacements for repetitive tasks and reduces downtime during production or repair work.

Suitable for

• Drilling hardened steels and alloy steels
• Metal fabrication and workshop drilling
• Maintenance, repair and overhaul (MRO) operations
• Use with hand drills and drill presses for medium-diameter holes

Key specifications

• Material: cobalt-alloyed high-speed steel (HSS-E)
• Diameter: 8.5 mm
• Pack quantity: 10 pieces
• Tip type: twist drill geometry for metal cutting
• Intended use: drilling in steels and metal materials

How to use

Secure the drill bit in the chuck of a hand drill or drill press and tighten firmly. Select an appropriate cutting speed and apply steady feed pressure; for hardened steels use lower speeds and steady coolant or cutting fluid to reduce heat. Mark and center-punch the drilling location before starting to ensure accurate positioning. Withdraw the bit periodically to clear chips and, when required, reapply cutting fluid to maintain tool life and hole quality.

Usage recommendations

Use appropriate personal protective equipment, secure the workpiece, and select cutting parameters matching material hardness. For best results on hardened steels, use coolant and moderate feed rates; replace worn bits from the pack to maintain consistent hole quality and reduce risk of tool breakage.