Straight Flute vs Spiral Upcut Bit: Which One Should You Buy?

Side by side

Specifications are manufacturer rated, as published on each listing and collected 18 October 2026.

straight flute vs spiral upcut bit: how each one cuts

A straight flute bit cuts with edges that run parallel to the bit’s axis. The Freud examples describe double flute designs for grooving, edge-routing and general-purpose routing, with precision ground edges for smooth cuts. A spiral upcut bit winds its flutes around the body so the rotation pulls chips upward and out of the cut. The SpeTool example describes upcut spirals for smooth grooves, slots, plunge mortises and dados with a clean edge and bottom, and the EANOSIC example names side milling, end milling and finish machining. Do not read a general winner into this: the listings on each side state what they state, and a missing figure is a gap, not a loss.

Chip ejection and edge finish

Chips are the practical difference. The Freud 04-100 example credits its black I.C.E. coating with keeping the edge cooler, minimizing friction and improving chip evacuation. The SpeTool example credits its 2-flute spiral design with efficient chip removal and reduced heat buildup, and claims its results are better than straight bits; that is the maker’s claim, reported in neutral words, not a measured result. On finish, the Freud examples claim clean cuts in solid wood, plywood and composites, while the SpeTool example claims clean edges and bottoms. The EANOSIC example claims a clean surface with no glitches and a coated edge that keeps its sharpness.

Sizes and shanks

Match the shank to your collet before anything else. Three examples use a 1/4 in shank: both Freuds and the SpeTool. The EANOSIC example uses a 1/2 in shank, so it needs a 1/2 in collet. On diameter, the examples run 1/8 in (Freud 04-100), 1/4 in (SpeTool), 3/8 in (Freud 04-126) and 1/2 in (EANOSIC). On reach, the SpeTool runs 3 in total with 1-1/4 in of cutting length, and the EANOSIC runs 4 in total with 2 in of cutting length; the Freud 04-126 gives 2-11/16 in overall in its bullets. Router bits throw chips and fine dust, so wear eye protection and collect the dust at the source.

For more spiral options, see the best spiral router bits for hardwood, and for the downcut side of the family, upcut vs downcut router bit.

Choose a straight flute bit if

• You want simple grooving and edge routing in hardwood, softwood, plywood and composites.
• You run a 1/4 in collet and want 1/8 in or 3/8 in diameters.
• You value the Freud extras the listings state: kickback reducing design and computer balancing on the 04-126.

Choose a spiral upcut bit if

• You want the spiral to lift chips out of grooves, slots and mortises.
• You do side milling and finish machining; the EANOSIC listing names both.
• You need extra reach: 3 in total on the SpeTool example, 4 in on the EANOSIC example.

Project Match

FAQ: lasers and CNC

Should I buy a straight flute or a spiral upcut bit?

For simple grooving and edge routing in wood, the straight flute examples cover it. For grooves, slots and mortises where you want chips lifted out of the cut, the upcut examples fit. Match diameter and shank to your collet and your cut.

What does upcut mean on a router bit?

The flutes spiral so rotation pulls chips upward and out of the cut. The SpeTool listing describes upcut spirals cutting grooves, slots, plunge mortises and dados with a clean edge and bottom.

Can these bits cut metal?

Only the EANOSIC listing names metals: carbon steel, soft alloy steel, tool steel, cast iron and aluminum alloy. The other three examples state wood materials only.

What shank size do I need?

Three examples use a 1/4 in shank: both Freuds and the SpeTool. The EANOSIC example uses a 1/2 in shank, so it needs a 1/2 in collet.

Which example bit suits mortises?

The SpeTool listing names plunge mortises among its uses, with a clean edge and bottom. The Freud examples name grooving and edge routing instead.

Related: straight flute vs spiral router bit, two flute vs four flute end mill, best CNC router bits for hardwood and the CNC tooling hub.