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Chicago-Latrobe 40578 aircraft extension drill bit, black oxide finish, split point tip

Chicago-Latrobe

Chicago-Latrobe 40578 135 Degree NAS Aircraft Extension Drill

SKU CH-K1J5-20HAG

Aircraft extension drill with 135-degree split point for high-performance machining

  • Product typeDrill Bits
  • Main materialHAWA
  • 135-degree split point starts holes cleanly without walking
  • High-speed steel with black oxide resists wear and corrosion
  • 28-degree helix clears chips efficiently from deep holes
  • Aircraft-extension length reaches confined fastener locations
  • Fractional 5/16-inch size fits standard NAS-type applications

Chicago-Latrobe 40578 Aircraft Extension Drill

This 135-degree split-point drill bit is made from high-speed steel with a black oxide finish for aircraft maintenance and deep-hole drilling tasks. The 4xD design achieves a maximum drilling depth of 1 1/4 inches in a single pass. Machinists and aviation technicians use it for precise holes in tough alloys where standard bits wander or overheat.

Ideal For Deep Precision Drilling

The 135-degree point angle and split-point geometry reduce walking on hard materials, suiting professionals who need accurate starts without centre punching. Its extended length reaches confined cavities that shorter jobber bits cannot access. Buyers who need carbide tips for abrasive composites or coolant-fed holes for high-volume production should evaluate other tooling options.

135 Degree Split Point Geometry

The 135-degree split point centres the bit instantly on contact, eliminating the need for a separate pilot hole in most metals. This geometry distributes cutting forces evenly across two edges, reducing thrust load and heat buildup during the 1 1/4 inch maximum drilling depth. It is the primary feature determining whether this bit matches the material hardness and hole tolerance requirements of the job.

How it compares

Measured against everything we stock in Bits, Hole Saws & Accessory Kits, at today’s prices. Recalculated every night.

Price $22.99
Cheaper than about 58% of the 5,493 comparable items (median $27.99).

Specifications

Product
Brand nameCHICAGO-LATROBE
Product typeDrill Bits
Size & build
Main materialHAWA

Questions about this item

What shank size does the 40578 extension drill need to fit my drill chuck?

The 40578 is a 5/16 in fractional-inch drill bit, so it requires a chuck that accepts that shank diameter.

How do I use the 135 degree split point on the 40578 to start holes without a centre punch?

The 135 degree split point is self-centring; apply steady pressure at the marked location and the bit will start without wandering.

When should I replace the 40578 high-speed steel bit?

Replace the bit when the cutting edges become dull, chipped, or when drilling performance drops noticeably in the material being machined.

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