If you ever picked up one of those 100-piece-or-more security bit sets, you’ve probably run across this bit pattern and wondered, What type of screw does this fit? Browsing the Irwin site, I found the answer: Torq-Set — also know as Tee+Cross and offset cruciform. Apparently our friends in the aviation business see these all the time.
Torq-Set screws are supposedly tamper-proof, but not if you have the right driver bit. The offset cruciform design fits precisely in screw heads with less cam-out, and it can handle higher torque than the similar looking Phillips design. The ISO standard 7994:1985 specifies the parameters of the metric series.
Irwin makes Torq-Set bits in sizes #0 through #10. Their bits run a few bucks each, but many tool manufacturers make these bits, so you can find cheaper sets if you dig.