Spring washers or those toothed deformable ones like a gear cut on the inside of the circumference of a flat ring.
I have to be honest I do not do much at all myself mechanically (not any longer anyway) but I would always go like for like if I was doing so.
My DIY is limited to engine and cabin air filters; adding screenwash fluid to the tank; adding oil when the light appears (if indeed it does); wiper blades; tyre pressures (very fussy about this);replacing failed lamps (bulbs, if you want to use the wrong technical term) etc etc. All schoolboy stuff for me now :-D