Drill collars are the components of the drill string that provide the weight on the bit when drilling . They are thick-walled, hollow tubular machined from solid bars of steel (usually plain carbon) or non-magnetic nickel-copper alloy or other non-magnetic premium alloys. The outside diameter may be machined with helical grooves (spiral) to reduce the potential contact surface for differential sticking prevention.

Drill Collars dimensions are standardized by API 7 Specifications. The ISO 10407 Spec. is actually a draft.

DRILL COLLAR TYPES

Smooth

Spiral