The invention relates to a replaceable blade piece (1) of a working cylinder of a screen crusher, which as viewed from the side is substantially T-shaped. The blade piece has a frame portion (2) forming the vertical shaft of the T and a blade portion (3) forming the horizontal arm of the T, the longitudinally opposite front surfaces of which form the actual work surfaces (4). The frame portion (2) has a through hole (5) extending in the longitudinal direction of the blade portion (3). Into the frame portion (2) is formed, on the opposite sides containing the hole (5), a channel-like section (6), which extends in the vertical direction of the frame portion (2), between the edge areas (8, 9) of the side with the hole (5). The invention further relates to a replaceable blade piece holder (11) of a working cylinder of a screen crusher, said holder having a U-shaped frame portion comprising arm portions (12, 13), through which extends a longitudinal hole (15) of the frame portion, and a bottom portion (14) with a curved bottom connecting the arm portions (12, 13). On the opposite surfaces of the arm portions (12, 13), onto their middle area is formed a bulge (16), which extends in the vertical direction of the arm portion, travelling at the hole (15).