They can't wiggle free - the preload set on the NDS crank arm holds them in place.
I think you are referring to press fit two piece converters like these
@Howard started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
They can't wiggle free - the preload set on the NDS crank arm holds them in place.
I think you are referring to press fit two piece converters like these