Armboard
The armboard is one of the most recognisable parts on the LP12. It is the black rectangular piece that floats in the frame and where the tonearm is mounted on. On older LP12 turntables it features the very iconic "Linn Sondek" logo. Coincidentally the circle with the downwards pointing triangle is said to represent the single point bearing system used by the LP12.
The armboard is where the tonearm is mounted on and in turn the armboard is mounted, via three screws, to the sub-chassis. To a certain degree the armboard acts as a decoupling mechanism between the tonearm and sub-chassis. Many after-market options exist but many users will still gravitate to an original board to retain the iconic logo look and feel.
For comparison, here are the old and new armboards:
Tonearm
The type of tonearm mounted on an LP12 is usually a large determining factor of the status of the turntable. Apart from Linn-branded arms that have been fitted to LP12 turntables, such as the Basik, Ittok, Akito, and Ekos units, many other third-party brands have also featured such as SME, Mission, Mayware, Morch, Dynavector, Micro Seiki, and Jelco. An LP12 is sensitive to the weight of the tonearm and so it is not advised to attempt to fit particularly heavy arms on the turntable.