When in use, your trailer needs to be supported under the chassis frame so that the floor is rigid and the trailer does not tip. These stabilizing jacks are a classic accessory for vintage trailers. The aluminum die cast bases are lightweight and rustproof. And they are stackable when not in use to save space. The chrome plated screw and handle extends the jack from 11" to 17". Each jack can hold up to 6000 lbs. Choose from either 2 or 4 jacks.