Chicago-Latrobe 40590 135-degree NAS aircraft extension drill bit

Chicago-Latrobe 40590 NAS extension drill

This Chicago-Latrobe 40590 is a 135-degree NAS-type aircraft extension drill bit made from HAWA-grade high-speed steel with a black oxide finish. It features a split point design for accurate starts and reduced walking on tough materials. The tool is built for precision drilling in aerospace and machining applications where performance matters.

Upgrade from standard bits for deep holes

Standard jobber drills lack the reach and specialised geometry needed for deep-hole work in aircraft structures. This extension bit provides a 4xD drilling ratio and a 28-degree helix angle suited for chip evacuation at depth. The jump is worth it when drilling 1/2 inch holes up to 2 inches deep in high-performance alloys where rigidity and accuracy are critical.

Straightforward chuck fit with depth care

The fractional inch shank fits standard drill chucks and collets without adapters. Install by securing the shank fully and running at appropriate speeds for high-speed steel in the target material. What usually goes wrong is insufficient chip clearing at maximum depth or excessive feed pressure causing the split point to chip or the extension to deflect.