Les Backshall wrote:... Gotoh premium 510 series have hollow aluminium rollers. No difference in how they work, but not as aesthetically pleasing to my mind.
I do like them. No wear, very robust and reliable. Such aluminium rollers have been in the market for more than 70-80 years. My 1956 Herwig had Rubner tuners with such rollers and I do remember pictures of 1940's Weissgerber guitars with similar ones. Der Jung are offering aluminum rollers with teflon bearing in black on their premium tuners, which might be a bit more aesthetically pleasing.
BTW most or all plastic rollers are not entirely from plastic! They do have a metal core where the shaft and thread for the joint to the gearwheel is applied. Depending of the qualtity of the meachines this metal core extends over the entire roller length. Presumably a 6 mm brass roller with a tightly fitted plastic sleeve to adjust the roller diameter to the higher elongation of plastic strings!? The hollow rivets which can be seen above in the rollers of Scheller tuners are to avoid slippage of the plastic sleeve!