Mount under motors to stop damage when the quad slides along on hard surfaces. 19x12 for 3mm screws for larger motors. 16x12 for 2mm 1806 and similar motors.
Added 14mm high version for Nighthawk.
Added 16x16 Skid for the newer motors.
These will also fit 23xx, 24xx and 25xx motors, check your motor layout first though.
Use a setting that gives a strong bond, I use .25mm and a reasonably fine hex pattern internally.
Motor screws go through skid, use a little Loctite to hold the motor in place, do not overtighten, the screws only need to be firm to hold the motor in place. The inset is 2mm so you will need 2mm longer screws, make sure you check that the screws do not go through the motor casing and damage the windings, screws should not need to screw in to the motor more than 2mm, if they are any longer get shorter ones or cut them off. For a 2204 motor and 3mm thick arm you should use 7mm screws, 8mm should also be fine but check the clearance.