SPECIAL DRILL COLLAR FEATURES
The bores are held to close tolerances by trepanning and are drifted to API specifications. The outside surface is “as-rolled”, which is the original mill finish. Connections are machined to API specifications and monogrammed with the API symbol. Connections are also kemplated to prevent galling.
Thread roots are “cold rolled” to provide longer fatigue life. Steel drill collars are offered both in a slick and spiral O.D. Spiraling the collars reduces wall contact between the drill collar and the wall of the hole to prevent differential wall sticking.