If you need hardware and will not hang the warping board on a wall, you can buy the hardware bag here.
If you wish to hang the warping board on a wall, use anchors or toggle bolts suitable for your wall material.
You can use any screw size that will fit the holes in the corners of the warping board and the wall anchors you've chosen. You may need screws longer than the ones that come with anchors—they have to go through the wood sides (about 1-1/8" thick) and into the anchor.
Instructions below assume you are using the included hardware and tell you to insert the machine screws from the back of the warping board. To hang on a wall, insert fasteners from the front of the warping board.