This bearing unit provides a rotating support with a bore diameter (d) of 50 mm, allowing shaft mounting at this size. The housing and shaft dimensions can be read from the catalogue drawing: A = 405 mm, D = 120 mm, H = 80 mm, J = 170 mm, L = 210 mm, N = 20 mm, V = 80 mm, W = 55 mm, X = 25 mm, b = 70 mm, A1 = 328 mm, H1 = 160 mm, H2 = 25 mm, J1 = 295 mm, L1 = 645 mm, L2 = 371 mm, and da = 55 mm. The unit belongs to the BL series and is identified under the catalogue symbol BL 55, produced by HFB. The housing dimensions listed above define the mounting footprint and bolt spacing, so they should be checked against the installation drawing before fitting. The bore diameter of 50 mm sets the shaft fit at the mounting point, while the outer housing dimensions (A, A1, L, L1, L2) determine the space required for installation and the position of the fixing holes. As no interchange references are given for this symbol, mounting should be based solely on the dimensions provided here.