An annular dust bonnet for a gyratory crusher , the dust bonnet being configured to facilitate alignment between a mainshaft assembly and a bore of an eccentric or eccentric liner upon introduction of the mainshaft assembly into the gyratory crusher by lowering the mainshaft assembly from above the gyratory crusher into the gyratory crusher ; the dust bonnet comprising: an inner sidewall configured for receiving a lower mainshaft of the mainshaft assembly therethrough; and an outer sidewall configured for engaging an annular dust seal provided within the mainshaft assembly ; the dust bonnet being CHARACTERISED IN THAT it further comprises a plurality of guides arranged radially-inwardly with respect to the inner sidewall , each of the plurality of guides having a guiding surface configured to contact the mainshaft assembly ; the guiding surface forming an angle with respect to the inner sidewall such that a lower portion of each guiding surface is positioned further radially-inwardly with respect to the inner sidewall than a respective upper portion of each guiding surface ; the guides collectively being arranged and configured to bias the lower mainshaft into concentric alignment with the bore when the mainshaft assembly is lowered into the gyratory crusher ; the dust bonnet further comprising a plurality of guide mounts provided to the inner sidewall , each of the guide mounts being configured to support and supporting a respective one of said guides in at least a radial direction wherein the dust bonnet comprises a lower sidewall extending radially inwardly with respect to the inner sidewall ; the lower sidewall forming an inner annular lip or inner annular flange proximate a lower portion of the dust bonnet ; and wherein the guide mounts are generally configured as triangular prisms or gussets. an inner sidewall configured for receiving a lower mainshaft of the mainshaft assembly therethrough; and an outer sidewall configured for engaging an annular dust seal provided within the mainshaft assembly ; the dust bonnet being CHARACTERISED IN THAT it further comprises a plurality of guides arranged radially-inwardly with respect to the inner sidewall , each of the plurality of guides having a guiding surface configured to contact the mainshaft assembly ; the guiding surface forming an angle with respect to the inner sidewall such that a lower portion of each guiding surface is positioned further radially-inwardly with respect to the inner sidewall than a respective upper portion of each guiding surface ; the guides collectively being arranged and configured to bias the lower mainshaft into concentric alignment with the bore when the mainshaft assembly is lowered into the gyratory crusher ; the dust bonnet further comprising a plurality of guide mounts provided to the inner sidewall , each of the guide mounts being configured to support and supporting a respective one of said guides in at least a radial direction wherein the dust bonnet comprises a lower sidewall extending radially inwardly with respect to the inner sidewall ; the lower sidewall forming an inner annular lip or inner annular flange proximate a lower portion of the dust bonnet ; and wherein the guide mounts are generally configured as triangular prisms or gussets. <EOS>