Taper Length Drills (Long Straight Shank)

What it is

Taper length is a straight-shank twist drill series in ANSI B94.11M that is longer than jobber length for the same diameter. The flute and overall lengths are similar to those of a Morse taper shank drill of the same size, which is where the name comes from. The closest metric series is DIN 340 (long series), which follows ISO 494. These drills are used for holes deeper than a jobber can reach while still holding the tool in a standard drill chuck or collet.

How to identify

A taper length drill has a plain straight shank and a body that is noticeably longer than a jobber of the same diameter. It has no Morse taper and no tang. Packaging may say "taper length," "TL," "long series" or "DIN 340." If the shank is tapered and has a flat tang at the end, it is a taper shank drill, which is a different product.

Taper length vs related products

Key points

• Long drills flex. Start the hole with a shorter drill or spot drill, then follow with the taper length drill.
• Reduce feed when entering and when breaking through. Long drills are more likely to wander and grab.
• Peck drill to clear chips. Taper length flutes are long, but deep holes still pack.
• Check that the drill press or machine has enough daylight between the chuck and the table for the longer tool and the part.
• Exact lengths by diameter come from ANSI B94.11M, DIN 340 or the maker's catalog.

Common mistakes

• Shipping a taper shank drill when the order said "taper length." This is the most common mix-up in this category.
• Using a taper length drill to start a hole without a spot or pilot.
• Assuming DIN 340 and inch taper length drills are the same length.
• Choosing a taper length drill when an aircraft extension drill is needed to reach past an obstruction.

Governing standards: ANSI B94.11M (twist drills); ISO 494 and DIN 340 (long series). Manufacturer catalogs for exact lengths.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.