For the part 1974894 this means:wool felt, white with a density of 0,36 g / cm3Quality T4 means made from one board For the part 2578755 this meanswool felt, white with a density of 0.36 g / cm3, soaked with oil VP 916, dyed (colour of the oil, see 8038380)Quality T4 means made from one boardThis part is very important for proper function. Therefore, it is necessary to test whether "new" felts fit perfectly to the round bars and whether they are oiled.