Screw Threads

Metric threads to ISO standards and UNF threads are used. See below for thread identification. Fixings with damaged threads must always be discarded. Cleaning the threads with a die or tap impairs the strength and closeness of fit and is not recommended. Always ensure that replacement bolts are of equal strength to those removed. Do not allow oil, grease or jointing compound to enter blind threaded holes because the hydraulic action which would be generated when screwing in the bolt or stud could split the housing. Oil the thread lightly before tightening to ensures free running thread, except in the case of self locking nuts. Always tighten a nut or bolt to the recommended torque figure. Damaged or corroded threads will affect the torque reading. To check or retighten a bolt or screw to a specified torque figure, first slacken by a quarter of a turn, then retighten to the correct figure.