A450A - STANCHION LEAD BLOCK - CLEVISPart # = A. 450A Description = Stanchion mounted block w removable pin Length (mm) = 94 Line Dia (mm) = 8 10 (14 max) Bracket Dia (mm) = 25 Weight (g) = 69 Stanchion Mounted Plain Bearing Block With Removable Pin and Sheave A stanchion mounted block is a device which, as the name suggests, is typically mounted to the vertical stanchion on a yacht. It allows lines to then be led along the length of the boat without the need to fix anything on the deck.