locknuts
 

locknuts
when assembling our very large pumps we have to use a locknut arrangement on the tie bars that hold the pump sections together. the locknut arrangement comprises two machined nuts face to face on a thread (up to m80). one of the nuts is a full nut, the other is a half nut. which of these should be on the top, the full nut or the half nut and which of these should be torqued to the correct spec?
usually the full nut carries the total clamping force of the fastener and the shear nut (half nut) is installed last to "lock" the assembly. crude but effective. i have seen such properly installed assemblies back off in high vibration applications.
rod
according to the ajax fastener handbook the half nut is put on first and the full nut is put on second. a full explaination of the logic for this is in the handbook.