Every figure below is a manufacturer
specification read off the listing itself. The judgments are ours.
What the specification says
8 mm (0.31 in) shank, 32 mm (1.26 in) cutting length, up-cut spiral geometry, solid carbide, two per
pack.
Why spiral rather than straight
A straight bit chops; a spiral shears. The shearing action is quieter, leaves a
cleaner wall, and — because the flutes are helical — moves the waste along the
bit rather than compressing it into the cut. On a groove deeper than about 10 mm (0.39 in)
that difference decides whether the bit burns.
Up-cut pulls the waste out of the groove and pulls the workpiece down onto the table — good for deep cuts, bad for the top surface, which can fray. Down-cut presses the top fibers down for a clean edge and packs the waste into the cut, so it suits shallow work on veneered material. Owning one of each is the usual answer.
Will an 8 mm (0.31 in) bit fit my router?
Only if it has an 8 mm (0.31 in) collet. 6 mm (0.24 in), 8 mm (0.31 in), 1/4 inch and 1/2 inch are all in use and none is interchangeable — a 1/4 inch bit in an 8 mm (0.31 in) collet appears to fit and will be thrown. Check the collet, not the router model.
