sometimes, yes, just sometimes, when a DMM or some hand held instrument has to be replace the battery, the battery chamber and the lock screw are always gave myself trouble.
Today I almost lost the screw of a cheap AC clamp meter when opened battery cover. The price cheap does not means to be no room for improvement. And I had build more than required quantity just in case I need another improvement to different instrument.
Actually we want to buy these Retainer Washers, however, the price, the quantity and shipping cost constraints will became no justify to buy from anywhere.
tools and material: paper puncher or belt puncher, PET sheet of used packing
This is my idea and a modification done, this screw will no longer be able to jumps away, unless the battery cover was gone.