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Chicago-Latrobe 40478 aircraft extension drill bit, 135 degree split point, black oxide finish

Chicago-Latrobe

Chicago-Latrobe 40478 135° NAS-Type Aircraft Extension Drill 5/16 in HSS Black Oxide

SKU CH-342V-XJ7CS

135-degree split-point HSS drill bit with black-oxide finish for aircraft extension work

  • Product typeDrill Bits
  • Main materialHAWA
  • 135° split point starts on contact for accurate holes
  • High-speed steel with black oxide resists wear and corrosion
  • 28° helix clears chips efficiently in deep drilling
  • 4×D reach handles extended-depth aircraft work
  • 1-1/4 in maximum drilling depth suits structural tasks

Chicago-Latrobe 40478 Aircraft Extension Drill

This 5/16 inch drill bit uses high speed steel with a black oxide finish for corrosion resistance. The 135 degree split point reduces walking and starts holes cleanly in tough alloys. A 28 degree helix angle clears chips efficiently during deep drilling operations.

Suited for aerospace maintenance

Mechanics drilling rivet holes in wing structures or fuselage panels will value the NAS-type geometry and extended reach. Builders needing a standard jobber length bit for general workshop tasks should look at a different tool because this design prioritises deep-hole access over rigidity.

Sustained drilling in hard materials

High speed steel maintains cutting edges through repeated passes in aluminium and titanium alloys when lubrication is adequate. The 1 1/4 inch maximum drilling depth at 4xD means heat builds quickly in deep holes so peck cycles and coolant are essential to prevent premature wear.

How it compares

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

Price $13.99
Cheaper than about 80% 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 size drill chuck does the 5/16 in shank on the 40478 need?

The 5/16 in shank fits any standard drill chuck that opens to at least 5/16 in, which covers most 3/8 in and 1/2 in capacity chucks.

Will the 135° split point on the 40478 start cleanly in the work-hardened spots left by my older cobalt bits?

Yes, the 135° split point is designed to self-centre and reduce walking, so it enters hard or work-hardened material without a centre punch.

How can I confirm the 40478 is cutting correctly once I start drilling?

Look for short, curled chips in a straw-to-blue colour and a smooth hole wall; those show the 135° point and black-oxide finish are evacuating heat properly.

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