The Keel upgrade to the LP12 is a replacement subchassis, machined from solid aluminium. It builds on the Cirkus upgrade (now fitted as standard to new LP12s) but is not included as standard in 'regular' production LP12s. Linn claims that the Keel is an application of its "close-tolerance aluminium machining", first seen in the ingot casing of the "Sondek CD12" CD player. The Keel, along with the Ekos SE tonearm and Trampolin Mk.2 were three Special Edition upgrades for the turntable's 33⅓ birthday, 33⅓ being the standard rotational speed when playing LPs. Keel offers integrated armboard and tonearm collar and with its varying 'pocket' depths for consistent centre of gravity. Keel upgrade is available for Ekos SE & Ekos tonearms only. Although Keel upgrade is possible for Akito tonearm but not recommended due to collar limitation.