McDermott iPro Slim 5/16 x 18 Black Collar pool cue shaft. McDermott iPro Slim is a 12mm high-performance cue shaft. Joint Diameter is .840″. The iPRO shaft has an Octadic Laminated Shaft Construction that features eight spliced pieces of premium maple that are bonded together to form our most radial consistent shaft yet. The i-Pro’s Triple-Layer Carbon Fiber Core extends the full length of the shaft (from ferrule to joint), stabilizing the entire shaft for absolute control and predictability. This technology increases radial consistency, reduces vibration, and virtually eliminates the inconsistencies found in a traditional maple shaft.