Abstract: A holder (2; 22; 82) for coating drill with a ceramic coating by a vapor deposition process has a perforated outer wall (4; 24; 84) into which the drills are inserted with their tips projecting. The holder has a hollow interior in which support means locate the inserted drills parallel and with their tips projecting to the same extent. The support means may comprise a correspondingly perforated inner wall (8; 26; 86) and a back wall (10; 28; 88) against which the drills abut, the outer, inner and back walls being parallel to each other. In one configuration, the holder has a hexagonal plan form with alternate outer walls (4) perforated and each with associated inner and back walls (8, 10). The holder is provided with a lid (52) that shields the interior from ingress of the coating material but provides an air passage to assist cooling of the portions of the drills in the holder interior after the coating has been applied.

Abstract: A helical twist drill has fluted lands each having projecting from their radially outer faces a plurality of circumferentially spaced support margins. At least one of the support margins is asymmetrically spaced with respect to the other support margins.