It is magnets that hold it on, as stated in some books/other sources.
The question goes to say though, even though the magnets are selective toggle on/off, wouldn't they also catch spare bullet casings/other metal bits/shrapnel? --- I'm never wrong, only occasionally mistaken.
l0ve posted... Shouldnt then my grenades stick to these magnetic points when I lob them at people? Not speaking of plasmas OBVIOUSLY.
"Available on the Mk. IV, Mk. V, and Mk. VI, the magnetic strips are very small yet powerful magnets place on the legs, waist, and back of the suit and is used to hold any equipment with a magnetic property. The suit also contains an electromagnetic system on the boots of the MJOLNIR suit that allow its wearer to stay attached to a metal surface in Zero G environments and can be toggled on or off by the wearer."
That raises a very good question. I doubt that it would be some form of magnetic material in the weapons too, because Covenant weapons are magnetized onto the armor also, not just UNSC weapons.
My guess is that it's an over thought on the developers part. --- I'm never wrong, only occasionally mistaken.