Knurled a. : Full of knots; gnarled.

Knurled a. : Milled, as the head of a screw, or the edge of a coin.

Example:
Why do some of my 9mm ammo have a Knurled band around the casing?

Taxonomy
Knurling, knurl, roller, pattern, workpiece, knurled, wheels, knurling tool, free encyclopedia, Hand knurling, knurling tools, criss-cross, ridges, Rings, metal pin, diamond, pitch, repair method.

Defination from the web:
knurled object than would be provided by the originally-smooth metal surface. ... The outer surface of the metal pin is knurled so that the raised detail 'bites' into the plastic irrespective of whether the size of the hole in ...