Tri-Wing screwdrivers also referred to as triangular slotted features a triangular hole in the middle with three wings that branch off and are offset from each other. This type of fastener and screwdriver was used primarily in the aerospace industry, though it may turn up in other places and there are even some in precision sizes. It's not a common fastener so Klein, Wera and Wiha are your only options for the moment.
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