Brooks Cambium saddle T Nut and Torx Screw
Brooks Cambium line of saddles are put together with these small Torx screws. Like anything that uses screws, you should make sure that they're tight once in awhile with the torx tool (sold separately). For extra measure, it's a good idea to also use a little Blue Loctite.
To be clear, when you order one quantity of this item, you'll get both one T nut and one Torx screw.