Chicago-Latrobe 40570 135 Degree NAS Aircraft Extension Drill 3/16 in HSS Black Oxide

Chicago-Latrobe 40570 Aircraft Extension Drill

The Chicago-Latrobe 40570 is a 135-degree NAS-type aircraft extension drill made from high-speed steel with a black oxide finish. It features a 3/16 inch fractional drill bit size and a split point design for accurate starts. This accessory targets mechanics and technicians performing deep-hole drilling in aviation or structural maintenance tasks.

Split point geometry and depth constraint

The 135-degree split point reduces walking and improves centring on hard materials without a centre punch. Maximum drilling depth is limited to 3/4 inch, reflecting the 4xD design ratio for this diameter. The 28-degree helix angle supports chip evacuation in confined spaces but does not suit deep-hole applications beyond the stated limit.

Verify shank fit and material compatibility

Confirm that your drill chuck or collet accepts the straight shank of this extension bit before ordering. The high-speed steel construction with black oxide coating is intended for general-purpose machining in ferrous alloys; it is not rated for hardened steels or exotic alloys requiring cobalt or carbide substrates. Ensure the 3/16 inch size matches the hole specification for your fastener or rivet pattern.