The two main types of tonearm are the single bearing `Unipivot` type which uses an inverted casing rotating on top of a spike type bearing and the other type which uses two pairs of bearings, one to allow vertical movement and the other pair providing the horizontal rotation.
The main requirements for a tonearm are to at all times hold the cartridge\stylus in exactly the right position in relation to the record groove, with the correct downward pressure and have the least amount of resistance to the movement of the tonearm across the record. The tonearms own mass also needs to be small to allow the cartridges suspension to be able to correctly `ride` over the record groove modulations without the tonearms own weight preventing it from doing so just like a heavy car having too soft a suspension system trying to ride over the bumps.
More commonly either carbon fibre or a tapered design armtube is being used which provides low mass and a very stiff structure, together with very high tolerance bearings being used with virtually indetectable friction, this allows the cartridge to read the record groove in an near ideal environment. As expected, due to the microscopically small vibrations being picked up by the stylus the better quality materials being used and the better the quality of manufacture and design of the tonearm then the better the sound quality will be heard.